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INDICATOR PRACTICE 



AND 



Steam -Engine Economy. 



WITH PLAIN DIRECTIONS FOR ATTACHING THE INDICA- 
TOR, TAKING DIAGRAMS, COMPUTING THE HORSE- 
POWER, DRAWING THE THEORETICAL CURVE, CAL- 
CULATING STEAM CONSUMPTION, DETERMINING 
ECONOMY, LOCATING DERANGEMENT OF 
VALVES, AND MAKING ALL DESIRED DE- 
DUCTIONS; ALSO TABLES REQUIRED 
IN MAKING THE NECESSARY COM- 
PUTATIONS, AND AN OUTLINE 
OF CURRENT PRACTICE IN 
TESTING STEAM-ENGINES 
AND BOILERS. 




BY 



FRANK F. HEMENWAY, 



Associate Editor "American Machinist," Member American Society 
Mechanical Engineers ; etc. 



jFulls JMustratefr, 



NEW YORK: 
JOHN WILEY & SONS. 

1886. 







• rtts 



Copyright, 1885, by 
John Wiley & Sons. 



PREFACE. 



DURING the past two years I have written several 
short articles for the American Machinist on the sub- 
ject of the indicator-diagram. In these there was not 
much attempt at connection, or intention to cover 
more than a few points as they came up from time to 
time. As an outcome of the appearance of these 
articles I have received many letters of inquiry, espe- 
cially from engineers in charge of steam engines and 
boilers of various classes. These letters, very fre- 
quently leading to considerable correspondence, have 
largely guided me in the preparation of this work : it 
seemed a fair presumption that they indicated what 
would be acceptable to others similarly situated. 

It has been my aim to present the subject compre- 
hensively enough to enable any engineer to apply the 
indicator to his engine, take the diagram, and make all 
necessary calculations from it. The endeavor has been 
to use no terms except such as are generally understood 
or fully explained, and no mathematical demonstra- 
tions are given or are required that involve the use of 
anything but simple arithmetical calculations. 

As one of the most important ends the indicator 
can serve is to point out how to bring about economy 
of steam-consumption, its use has been considered in 



IV PREFACE. 

connection with steam-engine economy: there seems 
to be no rational way of dividing these subjects even 
if it were desirable. 

A separate chapter has been devoted to locomotive- 
engines, because while the general matter applies to 
these in common with other steam-engines, there are 
some features peculiar to locomotive-indicating. 

All the engravings, both of diagrams and methods 
of obtaining drum-motion, were made expressly for 
this work. What was suitable of the matter referred 
to as written for the American Machinist has been re- 
vised and used ; the rest, comprising the larger portion 
of the whole, is now published for the first time. 

Fully believing that in the near future no engineer 
will be considered competent unless he has knowledge 
of the use of the indicator, I shall be satisfied if my 
efforts make the subject plainer to a few ; or if in any 
degree they assist those who recognize that the indica- 
tor-diagram has become so thoroughly incorporated 
with the current literature of steam-engineering, that, 
aside from the intention or ability to use the indicator, 
every one interested in the steam-engine should learn 

to read the diagram. 

F. F. Hemenway. 
New York City, Sept. i, 1885. 



CONTENTS. 



CHAPTER I. 

PAGE 

The Steam-Engine Indicator i 

Construction and Use of the Indicator — Ancient and Modern 
Construction — General Summary of the Operation of the In- 
dicator — Neutral Position of the Pencil -Some of the Ad- 
vantages of the Use of the Indicator — Forces which Move 
and which Oppose the Motion of the Piston of a Steam-En- 
gine — Wasted Power shown by the Use of the Indicator — 
Value of the Indicator to the Student of Steam Engineering 
— Care required in the Use of the Indicator. 

CHAPTER II. 

Definition of Technical Terms, 7 

Absolute Pressure — Boiler Pressure — Initial Pressure — Termi- 
nal Pressure — Mean Effective Pressure — Back Pressure — 
Total Back Pressure— Initial Expansion — Ratio of Expansion 
— Wire-drawing — Clearance — The Unit of Heat — The Unit 
of Work — Horse-power — Indicated Horse-power — Net 
Horse-power — Saturated Steam — Superheated Steam — Com- 
pression — Latent Heat — Sensible Heat — Piston Displace- 
ment. 

CHAPTER III. 

Getting Ready to take Diagrams, . . 10 

Drilling the Holes — Elbows— Long Pipes and Bends should be 
Avoided — Cleaning Pipes — Core Sand — Diagrams should be 
taken from both Ends of the Cylinder — Using Two Indi- i 



VI CONTENTS. 

PAGE 

cators — Preventing Radiation — Testing the Truth of Dia- 
grams taken with Long Pipe Connections — Taking Diagrams 
Simultaneously from both Ends of the Cylinder — Proper 
Spring to Use — Explanation of the Numbers on Springs — 
Care of Springs — Cleaning and Oiling the Indicator. 

CHAPTER IV. 
Drum Motion, . 16 

Where to take the Motion from — Examples of Drum Motions- 
Figs, i, 2, and 3 — Reducing Levers — Planning for Attaching 
the Indicator and Getting Drum Motion — Length of Dia- 
grams — Ad vantages of Long Diagrams — Best Cord to Use — 
Hooks and Rings. 

CHAPTER V. 

Taking the Diagrams, . . . . . . . 23 

Adjusting the Length of Cord — Adjusting the Paper and Pen- 
cil — Pencil Stop — Tracing the Atmospheric Line — Ascertain- 
ing if the Indicator is working properly — Memoranda neces- 
sary — Printed Blanks. 

CHAPTER VI. 
Reading the Diagram, .26 

Absolute Information conveyed by the Figure traced — Theo- 
retical Considerations — Names of the different Lines of the 
Diagram — Fig. 4 — The Atmospheric Line — Importance 
of correctly establishing the Atmospheric Line — Line of 
Perfect Vacuum — The Admission Line — The Steam Line — 
The Expansion Line — The Exhaust Line — The Line of 
Counter-pressure — The Compression Line — Points and Peri- 
ods in the Stroke of the Piston — Data Necessary and Useful 
— The Use of- the Indicator for Adjusting Valves — Lead — 
Late Admission — Argument for Early and for Late Admission 
— Fig. 5 — Early and Late Exhaust Closure — Fig. 6 — Com- 
pression — Early Exhaust Opening — Back Pressure — Pound- 
ing — Wavy Lines — Serrated Lines — Figs. 7 and 8 — Tight In 
dicator Piston. 



CONTENTS, VII 



CHAPTER VII. 

PAGE 

Heat — The Expansion of Steam, 38 

Heat and Work — Heat of Combustion of Coal — The Conver- 
sion of Water into Steam — Example of Evaporation — Mari- 
otte's Law — Example of Expansion — Rule for Finding the 
Mean Pressure of Expanding Steam — Ratio of Expansion — 
Economy of Expansion — The Economy of High Pressure — 
Example — Fig. 9. 

CHAPTER VIII. 

Computing the Horse-power, 48 

Finding the Mean Effective Pressure — Figs. 10 and n — Dia- 
grams from both Ends of Cylinder should be Calculated — 
Measuring by Ten or More Divisions — Precautions in Meas- 
uring the Diagrams — Horsepower for One Pound Mean 
Effective Pressure. 

CHAPTER IX. 
The Theoretical Curve, . . . . . . .55 

Reasons for Establishing the Theoretical Curve — Fig. 12 — 
Points from which to Draw the Theoretical Curve — Differ- 
ent Methods of Drawing the Curve — Figs. \i\ and 13 — Lo- 
cating the Clearance Line on the Diagram — Professor 
Sweet's Plan for Measuring Clearance. 

CHAPTER X. 
Measuring from the Diagram the Steam Exhausted, 65 

Steam Exhausted per Hour — Fig. 14 — Steam Saved in Clear- 
ance Space — Steam Exhausted per Horse-power per Hour — 
Causes for Disagreement of Theoretical and Actual Curves 
— Leaky Steam Valve — Computing Steam exhausted by 
Means of Thompson's Table — Thompson's Computation 
Table— Fig. 15. 



V1U CONTENTS. 



CHAPTER XL 

PAGE 

Condensing Engines, 74 

Diagrams from a Steam-Jacketed Cylinder — Fig. 16 — High 
Terminal Pressure — Diagrams from an Engine Condensing 
and Non-condensing compared — Fig. 17 — Too much In- 
side Lap — Condenser Pressure — Faulty Exhaust Pipe — Back 
Pressure — Compound Condensing-engine Diagrams — Figs. 
18, 19, and 20. 

CHAPTER XII. 
Diagrams Representing Various Peculiarities, . 90 

Improper Action of Cut-off Valve, and Restricted Exhaust — 
Fig. 21 — Estimating Clearance — A Wasteful Engine — 
Changes that the Indicator would have pointed out — Pecu- 
liar Expansion Lines — Reopening of Steam Valve — Fig. 22 
Rapid Fall of Expansion Curve — Figs. 23 and 24 — Eccentric 
Out of Place — Impossible Admission and Expansion Lines 
—Fig. 25. 

CHAPTER XIII. 
Initial Expansion — Small Steam-pipe, . . . 104 

Economy of Initial Expansion — Fig. 26 — Straight Steam Lines 
— Distinction between Initial Expansion and Throttling — 
Throttling and Automatic Engines — Diagrams from the 
same Engine with Large and Small Steam Pipes — Figs. 27 
and 28 — Advantages of Large Steam Pipes. 

CHAPTER XIV. 
Detecting Leaky Valves — Light Fly-wheels, . .111 

Fig. 29— Late Exhaust— Work not Equal in the two Ends of 
the Cylinder — Effect of Leakage on the Diagrams — Fig. 30 — 
Wasteful Effects of a Light Fly-wheel — Improper Action of 
Governor. 



CONTENTS. IX 



CHAPTER XV. 

PAGE 

Diagrams from Locomotive Engines, . . . .119 

How to Connect the Indicator — The Drum Motion — Descrip- 
tion of Reducing Motion — How to Preserve the Data — 
Safety Precautions — Diagrams representing Good Practice 
— Too much Compression — Moderate and High Speed com- 
pared — Comparison of Losses — Loss from Back Pressure — 
Economy of the Link Motion — Nozzle and Exhaust Openings 
— Steam Consumption measured from a Locomotive-engine 
Diagram — Finding the Horse-power — Horse-power for One 
Pound Mean Effective Pressure and One Revolution per 
Minute — The Effect on the Diagram of the Steam Distribu- 
tion peculiar to the Locomotive — Figs, 31, 32, 33, 34, 35, 36, 
37, 38, 39. 40, 4i, and 42. 

CHAPTER XVI. 

Other Uses of the Indicator, 139 

Steam-chest Diagrams — Diagrams from Pumps — Good and 
Bad Practice — Figs. 43, 44, and 45. 

CHAPTER XVII. 
Steam engine Economy, 145 

General Considerations — Point of Cut off — Underloaded En- 
gines—Atmospheric Resistance — Reduction of Speed — Fly- 
wheel—Rule for Weight of Rim of Fly-wheel— Working 
with Lower Steam Pressure — Throttling— Checking Results 
of Weighing Coal— Overloaded Engines— Increasing the 
Speed— Working with higher Steam Pressure— Adding a 
Condenser — Heating Feed-water. 

CHAPTER XVIII. 

Tables, . , . ,153 

Table I . Areas of Circles in Square Inches — Table II., Proper- 
ties of Saturated Steam — Economy of Heating Feed-water — 



X CONTENTS. 

PAGE 

The Evaporative Duty of Boilers— Table III., Hyperbolic 
Logarithms -\- i — Table IV., Common Fractions with their 
Decimal Equivalents. 

CHAPTER XIX. 

Testing Engines and Boilers, 168 

Absolute Exactness not possible — Different Ways of Making 
Tests — Determining the Coal Used per Horse-power per 
Hour — Measuring the Indicated Horse power — Another 
Plan of determining the Coal burned — Water per Horse- 
Power — Objection to Water Test — Pumping engine Duty 
and Tests — Boiler Tests — Table for Reducing to Standard 
the Observed Evaporation of a Boiler — What should be 
noted. 



INDICATOR PRACTICE AND STEAM-ENGINE 
ECONOMY. 



CHAPTER I. 
THE STEAM-ENGINE INDICATOR. 

CONSTRUCTION AND USE OF THE INDICATOR. 

The steam-engine indicator is an instrument for 
measuring and recording pressures. It is said to have 
been invented by Watt, and employed as a means of 
improving his engines. In its earlier forms the indi- 
cator was crude — hardly up to the standard of the 
engines upon which it was used. As made at present, 
it is as nearly perfect as it can be expected any analo- 
gous piece of mechanism will be. Its records are uni- 
versally relied upon, and deductions intelligently made 
from these records are correct within the limits of 
present knowledge of steam-engineering. With the 
comparatively rude instruments used only a few years 
ago work was done that resulted in great improvement 
of the steam-engine. With the modern indicator, so 
nearly perfect in its action, improved as it has been 
found absolutely necessary to improve it for modern 
high speeds and pressures, the behavior of steam in 



2 INDICATOR PRACTICE. 

the cylinder and in getting into and out of it has been 
determined and studied in a way to add greatly to the 
general fund of knowledge in the science of steam- 
engineering. 

The most common use that is made of the indicator 
is for measuring continuously during the stroke of the 
piston the pressure in the cylinder of a steam-engine, 
and recording that pressure on a piece of paper, the 
record being called an indicator-diagram. The pencil 
or marking-point with which the diagram is traced is 
connected by suitable mechanism with a small piston 
adapted to be moved substantially frictionless in a 
cylinder. The connection is such that the pencil 
moves in a straight line up and down with the piston, 
the motion of the pencil being several — usually four 
or five — times greater than that of the piston. In use 
on a steam-engine the indicator is so placed that the 
cylinder below the piston is put in communication 
with one end of the cylinder of the engine by turning 
a small cock. The upper end of the cylinder of the 
indicator (above the piston) is always open to the at- 
mosphere; when the cock is turned to close the com- 
munication between the cylinders of the indicator and 
engine both ends (above and below the piston) of the 
indicator-cylinder are open to the atmosphere. 

NEUTRAL POSITION OF THE PENCIL. 

The motion of the piston of the indicator is con- 
trolled or restricted by a spring of known tension. 
When both ends of the cylinder are open to the at- 
mosphere the pencil will be held in its neutral posi- 
tion. When the cock is turned to make the connec- 



THE STEAM-ENGINE INDICATOR. 3 

tion between the cylinders of the indicator and the 
engine, if the pressure in the latter is greater than the 
pressure of the atmosphere, the indicator-piston, and 
with it the pencil, will be forced, against the resistance 
of the atmosphere and that of the spring, above the 
neutral position. When the pressure in the cylinder 
is less than that of the atmosphere the pressure of the 
latter will force the pencil below its neutral position, the 
downward motion of the indicator-piston being resisted 
by whatever pressure is in the engine-cylinder and by 
the spring. 

The paper-drum has a reciprocating motion on its 
axis, at right angles to the motion of the pencil. If 
with the indicator properly attached to the cylinder of 
the engine the paper is placed on the drum, the latter 
given a motion corresponding to that of the piston of 
the engine and the pencil held in contact with the 
paper, a diagram will be traced from which the pres- 
sure against one side of the piston of the engine for an 
entire revolution of the crank, or double stroke of the 
piston, may be measured. 

SOME OF THE ADVANTAGES OF THE USE OF THE INDICATOR. 

The piston of a steam-engine is moved by the pres- 
sure of steam against one of its sides. Its progress is 
resisted by a lesser pressure against its other side, by 
friction, and by the load upon the engine. The pres- 
sure operating to move the piston will always be less 
per square inch of surface than the pressure in the 
boiier or steam-pipe supplying the steam, to an extent 
proportionate to the degree of freedom with which the 
steam is permitted to pass to the cylinder. Lack of free- 



4 INDICATOR PRACTICE. 

dom in this respect may be in part due to insufficient 
steam-pipe or steam-port area, to bends or restrictions 
in the pipes or ports, to badly arranged or deranged 
valve-gear, and to other causes, and in part to the 
operation of the governor in maintaining a pressure to 
correspond with the load and desired speed. It. is of 
the first importance in the economical use of steam in 
the steam-engine to know the exact pressure in the 
cylinder throughout the entire stroke of the piston, and 
what influences the extent of this pressure. Without 
the use of the indicator this cannot be known. 

The resistance which the piston encounters is in part 
due to natural and unavoidable causes, and in part to 
construction and arrangement, subject to changes and 
modifications. In a condensing-engine this resistance 
will always be greater than the pressure in the con- 
denser, and in a non-condensing engine greater than 
the pressure of the atmosphere. Frequently the re- 
sistance in either case is materially greater than it 
should be, and sometimes enormously so. The indi- 
cator records this resistance, and if unduly great dur- 
ing any part of the stroke, enables the engineer to 
locate the trouble, and to determine the effect of the 
remedy he may apply. 

The use of the indicator also enables the engineer to 
know at any time the power the engine is exerting, 
and by this means to detect causes outside the engine- 
room through which steam is wasted. Shafts out of 
line, injudicious change of lubricants, defects in ma- 
chines and machinery — causes by which the work re- 
quired of the engine is increased — leave their mark 
on the diagram. Increased coal-consumption without 



THE STEAM-ENGINE INDICATOR. 5 

corresponding increase of work leads to a search for 
the cause. The regular use of the indicator is the 
only way in which the steam-engine can be kept at 
work economically in the use of steam. Engines have 
been run for years, wasting thousands of dollars in 
fuel, when the application of the indicator would have 
led at once to the detection of the cause of their 
wastefulness. 

To the student in steam-engineering the indicator is 
an invaluable assistant. Careful consideration of dia- 
grams from different engines, under varied conditions, 
cannot fail to lead to thought and investigation. Es- 
pecially is the indicator invaluable if the student must 
pursue his studies without much help from teachers. 
By its use many stumbling-blocks will be removed, 
while the calculations he will be impelled to make in 
connection with it will lead to the acquisition of a good 
general knowledge of the whole subject. 

CARE REQUIRED IN THE USE OF THE INDICATOR. 

Using the indicator is for the most part a matter of 
common-sense. It is a delicate instrument, and re- 
quires careful handling. So is a micrometer-caliper or 
any instrument of precision delicate in the same sense, 
and the judgment that applies to the use of one is 
equally applicable to that of the other. It should be 
fully appreciated that the entire value of the diagram 
depends upon its truthfulness: if there is any question 
of its quality in this respect, it is worthless. If it is 
supposed to be truthful, and is not so, it is worse than 
worthless, because misleading. In order that the dia- 
gram may be reliable the indicator must be kept in 



INDICATOR PRACTICE. 

perfect condition, and, when attached for use, the con. 
nection must be such that the pressure in the cylinders 
of the engine and indicator will instantly be equalized. 
It is equally important that the motion of the paper- 
drum shall correctly represent that of the piston of the 
engine. No one need expect to succeed in the use of 
the indicator unless he possess himself of the skill to 
properly attend to these details. They are such as 
will readily be understood by the skilled mechanic, and 
the necessary skill is quite within the reach of any one 
who is fit to have the care of a steam-engine. From 
lack not so much of skill as a complete appreciation of 
what is required, unsuccessful attempts to profitably 
use the indicator may be traced. The requisites are 
care in handling the instrument and the habit of think- 
ing — just what are required to properly handle an en- 
gine, or to do good work of any kind. With these, 
any one can learn to use the indicator without any in- 
struction except such as he may get by reading and 
study. 



DEFINITIONS OF TECHNICAL TERMS. 



CHAPTER II. 
DEFINITIONS OF TECHNICAL TERMS. 

Absolute Pressure of steam is its pressure reckoned 
from vacuum : the pressure as shown by an ordinary- 
steam-gauge, plus the pressure of the atmosphere. 

Boiler Pressure, or gauge-pressure, is the pressure 
above atmosphere : the pressure as shown by a correct 
steam-gauge. 

Initial Pressure is the pressure in the cylinder of an 
engine at or near the beginning of the forward stroke 
of the piston. 

Terminal Pressure (t) is the pressure that would be 
in the cylinder at the end of the stroke of the piston if 
the exhaust-valve did not open until the stroke was 
completed. It may be found by extending the expan- 
sion-curve to the end of the diagram. The theoretical 
terminal pressure is found by dividing the pressure at 
cut-off by the ratio of expansion. 

Mean Effective Pressure (M.E.P.) is the average 
pressure urging the piston forward during its entire 
stroke in one direction, less the pressure, that resists 
its progress. 

Back Pressure is the loss, expressed in pounds per 
square inch, due to getting the steam out of the cylin- 
der after it has done its work. On the diagram from 
a non-condensing engine it is indicated by the distance 



8 INDICATOR PRACTICE. 

apart of the atmospheric line and the line of counter- 
pressure ; on the diagram from a condensing-engine it 
is indicated by the distance apart of the line of counter- 
pressure and a line representing the pressure in the con- 
denser.* 

Total Back Pressure in either a condensing or non- 
condensing-engine is represented on the diagram by 
the distance between the line of counter-pressure and 
that of perfect vacuum. 

Initial Expansion is the fall of pressure in the cyl- 
inder of an engine as the piston advances and before 
steam is cut off. 

Ratio of Expansion is the proportion the total volume 
of steam in the cylinder — the exhaust not being opened 
till the end of the stroke — bears to the volume at cut- 
off. 

Wiredrawing is the operation, accidental or inten- 
tional, of reducing the pressure of steam between the 
boiler and cylinder. Wire-drawing generally, but not 
always, brings about initial expansion. 

Clearance is the space between the piston at the end 
of its stroke and the valve-face. It is usually reckoned 
in per-cent of the piston-displacement, or in its equiv- 
alent in length added to the cylinder. 

The Unit of Heat is the quantity of heat which must 
be added to one pound of water of a temperature just 
above the freezing-point to increase its temperature 
one degree Fahrenheit. 

* Back-pressure in a condensing-engine is usually spoken of as 
reckoned from vacuum: this is not correct, as the engine must ex- 
haust against an artificial atmosphere in the condenser, which may be 
more or less, according to circumstances. 



DEFINITIONS OF TECHNICAL TERMS. 9 

The Unit of Work — foot-pound — is one pound lifted 
to a height of one foot. One unit of heat is equal to 
772 units of work. 

A Horse-power (H.P.) is 33,000 pounds lifted to a 
height of one foot in one minute of time, or equivalent 
motion against resistance. 

Indicated Horse-power (I. H.P.) is the horse-power as 
shown by the indicator. It is the product of the mean 
net area of the piston, its speed in feet per minute, 
and the mean effective pressure, divided by 33,000. 

Net Horsepower is the indicated horse-power less the 
friction of the engine. 

Saturated Steam, frequently called " dry steam," is 
steam that contains just sufficient heat to maintain the 
water in a state of steam. When saturated steam suf- 
fers any loss of heat,., some of the steam will be con- 
densed. 

Superheated Steam is steam which has an excess of 
heat : this excess may be parted with without conden- 
sation. 

Compression is the action of the piston in compress- 
ing the steam remaining in the cylinder at exhaust- 
closure into the clearance-space. 

Latent Heat of steam is the quantity of heat, ex- 
pressed in heat units, required to vaporize or evapo- 
rate water already heated to the temperature of the 
steam into which it is to be converted. 

Sensible Heat of steam is its temperature as shown 
by a thermometer. 

Piston Displacement is the space, usually reckoned in 
cubic inches, swept through by the piston in a single 
stroke. It is found by multiplying the area of the 
piston in inches by the stroke in inches. 



IO INDICATOR PRACTICE. 



CHAPTER III. 
GETTING READY TO TAKE DIAGRAMS. 

HOW TO ATTACH THE INDICATOR. 

The use of the indicator has become so common 
that the cylinders of nearly all engines are drilled and 
tapped for its attachment by the builder, as few build- 
ers are willing to leave their engines in the hands of 
the user until after the adjustment of valves by its aid. 
If the cylinder has not been drilled, the first thing in 
order is to attend to it. The cock furnished with the 
indicator is threaded for half-inch gas-pipe tap, and un- 
less the conditions are such that considerable length of 
pipe must be used, the cylinder should be tapped to 
correspond. If a horizontal engine, the holes may be 
drilled in the top or side of the cylinder, or in the 
heads, as is most convenient for attaching the indicator 
and getting motion to the drum: they should never 
be located at the bottom, where they will take water 
instead of steam, nor where the openings will be ex- 
posed to direct currents of steam from the ports. If 
on the top or side, they should be so near the ends of 
the cylinder that the piston at the extremes of its 
travel will not cover them. Occasionally it may be 
necessary to channel the head or counter-bore of the 
cylinder a little to provide free opening at all times. 



GETTING READY TO TAKE DIAGRAMS. II 

Drilling holes so they are covered by the piston at 
extreme travel sometimes results in puzzling diagrams. 
When the holes are on top of the cylinder, the cocks 
may sometimes be screwed directly into them, but 
generally it will be necessary to use a short nipple and 
coupling to reach through the lagging. When in the 
side, a nipple and elbow or a bent pipe should be used 
to carry the indicator a little away from the cylinder 
and set it in an upright position. The indicator may 
be set horizontally, when setting it so cannot well be 
avoided ; but it is always better to set it vertically when 
practicable to do so. If an elbow is used, it is better 
for being of a radius four or five times greater than 
that of an ordinary elbow. It is a good plan to have 
four such elbows made, cast in brass ; they are likely 
to be of use some time when it is necessary to make 
more than one turn in a pipe. If such elbows are not 
at hand, a very good substitute may be provided by 
bushing three-quarter-inch elbows. In vertical engines 
it is best to drill the holes in the side of the cylinder. 

LONG PIPES AND BENDS SHOULD BE AVOIDED. 

In locating the indicator, the endeavor should always 
be to use the least admissible length of pipe and the 
fewest bends practicable. Although steam travels 
with great rapidity, it nevertheless takes time to fill 
long lengths of pipe, and the current is checked in pass- 
ing elbows and bends. All pipe and fittings should be 
free from scale and dirt, and no putty or lead used in 
making the joints. A little tallow on the pipe-threads 
will do no harm, but none should be used in the fittings. 
Before putting the indicator in place, the pipe should 



12 INDICATOR PRACTICE. 

be blown through with steam to dislodge any foreign 
matter that may be inside it, which otherwise might 
find its way into the cylinder of the indicator. The 
cylinder and piston of the indicator are easily injured 
by grit or dirt, hence it is essential to see that the pipes 
are free and clean. For similar reasons it is not advisa- 
ble to use an indicator on a new engine until it has 
been under steam long enough to dislodge and get rid 
of core sand. All reasonable precautions should be 
taken to prevent anything except clean steam and the 
oil used finding its way into the indicator-cylinder. 

DIAGRAMS SHOULD BE TAKEN FROM BOTH ENDS OF THE 

CYLINDER. 

It is necessary for all purposes to take diagrams 
from both ends of the cylinder. When two indicators 
are used one may be attached to each end, and dia- 
grams taken nearly simultaneously. If only one indi- 
cator is used, it must be changed from end to end, or 
the two ends piped together with a three-way cock at 
the centre of the cylinder, into which the indicator- 
cock is screwed. Instead of the three-way cock, a tee 
may be used with a straight-way cock each side of it. 
When connected in this way, if the cylinder is more 
than ten inches diameter, or unless the piston speed is 
quite slow, it is advisable to use three-quarter-inch 
pipe. With small cylinders the extent of the valve- 
opening is correspondingly small, and it will be better 
to use half-inch pipe with easy bends or large elbows 
than to depend upon filling the large pipe at the very 
beginning of the stroke. The pipe may be wound 
with woollen cloth to partially prevent radiation. 



GETTING READY TO TAKE DIAGRAMS. 1 3 

If there are doubts about the truthfulness of the 
diagrams taken when long pipes are used, they may be 
verified or set at rest by comparison with diagrams 
taken from one end with the indicator closely con- 
nected. It is undoubtedly true that the use of suf- 
ficient pipe to connect the two ends of the cylinder 
will have some effect on the diagram, but the effect has 
been very much overstated and over-estimated. Under 
ordinary conditions it will be slight. Still, when prac- 
ticable, it is better to use two indicators, or, generally, 
to change one from end to end. This last-named plan 
is open to the objection that in automatic engines the 
point of cut-off may change while the indicator is being 
moved, or that in any engine the load may vary 
materially in the interval. This is important when it 
is desired to find the exact load upon an engine at a 
particular instant, as in the instance of a rolling-mill 
engine when the piece is passing the rolls. For such a 
purpose two indicators should be used, handled by two 
persons. 

It is convenient when adjusting the valves of an 
automatic cut-off engine to take diagrams simultane- 
ously from each end, especially when adjusting to 
secure equalized cut-off. But with many engines it is 
possible to arrange so as to conveniently note the posi- 
tion of the governor when indicating one end, and then 
compare a diagram taken from the other end when the 
governor is in exactly the same position. Where a 
large number of diagrams are taken at intervals, as in 
determining the average power developed, no error 
will arise from changing the indicator from end to end, 
even though the power be variable. While the use of 



14 INDICATOR PRACTICE. 

two or even more indicators is frequently a matter of 
some convenience, by the exercise of a little judgment 
one may be made to serve every ordinary purpose. 

PROPER SPRING TO USE. 

Springs of different tension to suit different condi- 
tions as to steam-pressure, speed, etc., should be kept 
on hand. The numbers on the springs signify that a 
vertical movement of the pencil of one inch is accom- 
plished by a pressure per square inch equal to the num- 
ber of the spring. Thus, if a 40 spring is used, a pres- 
sure in the cylinder of 40 pounds per square inch will 
raise the pencil I inch, or a pressure of I pound will 
raise it fa inch, and so on. For convenience in meas- 
uring pressures from the diagram, scales of pounds 
corresponding to the different springs are provided. 
But, as will be readily understood, measurements may 
be made with an ordinary scale of inches. 

For speeds commonly found in practice, springs 
numbered about one half as high as the steam-pres- 
sure employed may be used ; for 80 pounds boiler-pres- 
sure use a 40 spring, and in that proportion for other 
pressures. In cases of quite high speeds, however, it 
is often advisable to use proportionately stronger 
springs, say in extreme cases a 50 or 60, or even an 
80 spring, for 80 pounds boiler-pressure. When the 
initial-pressure is materially less than boiler-pressure, 
proportionately lighter springs may be used. In re- 
spect to the strength of the spring, it is advisable to 
use one strong enough to insure a reasonably smooth 
diagram, but light enough to get a fairly large one. 

A spring numbered one half as high as the boiler- 



1 



GETTING READY TO TAKE DIAGRAMS. 1 5 

pressure may be the rule, to be varied as the judgment 
and experience of the operator shall dictate. 

CARE OF SPRINGS. 

Care should be taken not to allow the springs to 
rust. Even if nickel-plated, rust may attack them in 
spots. To guard against this they should never be 
left in the indicator when not in use; remove them, 
wipe carefully, and wrap in a piece of tissue-paper, 
well oiled. 

CLEANING AND OILING THE INDICATOR. 

After use, the inside of the cylinder of the indicator 
should be wiped quite clean and dry with a piece of 
soft waste on a stick or long pencil. It should nevei 
be put away dirty. Before use the cylinder should be 
well oiled, using oil of the best quality. A little oil 
should also be applied to the joints. 



l6 INDICATOR PRACTICE. 



CHAPTER IV. 
DRUM MOTION. 

WHERE TO TAKE THE MOTION FROM. 

The motion for the paper-drum is very commonly 
and conveniently taken from the cross-head, reduced 
to give the length of diagram desired. In beam-en- 
gines it is frequently taken from the beam. No plan 
for reducing the motion from the cross-head is univer- 
sally applicable ; circumstances must determine what 
plan can best be employed, and good judgment used 
in getting a motion that will, on a reduced scale, repre- 
sent that of the piston. A few examples are given 
which will suggest others to suit existing conditions. 
Referring to these, in Fig. I the reducing lever a is 
pivoted overhead to a temporarily arranged plank or 
timber, which may be extended down from the over- 
head flooring, or it maybe a scantling braced from the 
top of the engine-bed to the ceiling — any arrangement 
that will present a suitable surface at the proper height. 
The segment b is made fast to the lever so that its 
semi-circumference is true with the pivot/* upon which 
the lever swings, but may be set at any angle with the 
lever. The radius of b must be such as to give the re- 
quired reduction of motion ; that is, the radius should 
bear the same proportion to the length of the lever as 
the proposed length of diagram bears to the stroke 



DKUM MOTION. 



17 




IS INDICATOR PRACTICE. 

of engine. The radius may be readily found by multi- 
plying the length of the lever by the proposed length 
of diagram, and dividing by the stroke of the piston. 
For instance, suppose the length of diagram is to be 
4 inches, the stroke of piston being 24 inches, and the 
length of lever 40 inches : 40 X 4 = 160, which divided 
by 24 gives for radius of b 6 T 8 g- inches. 

At the lower end the reducing-lever is connected by 
a short connection c to a pin fast in the cross-head, or 
in an angle-iron made fast to the cross-head. 

The lever a may be of any convenient length, not 
less than about one and one half times the stroke of 
the engine. The length of connection c may be about 
one half the stroke of the engine, more or less. When 
the cross-head is at mid-stroke the lever # should stand 
in a vertical position, and the connection c should, 
during the stroke of the engine, vibrate equally above 
and below a horizontal position. 

With this arrangement the cord d may be led to the 
indicator in any direction in line with the swing of the 
lever a, the piece b being moved, if necessary, to ac- 
commodate the direction ; it is evident that the mo- 
tion would not be changed except in direction, which 
is immaterial, if b were turned one half around from 
the position in which it is shown, bringing the arc at 
the top. Two cords may be led from b to as many 
indicators, if desired. 

An objection to this reducing motion is that the 
piece b must be turned true, and then will not suit 
different conditions as to stroke, etc. But if the lever 
a always bears the same proportion in length to the 
stroke of the engine on which it is used, which in the 



DRUM MOTION, 1 9 

majority of instances it may be made to do, then the 
same piece b will give diagrams of the same length, no 
matter what the stroke of the engine is. By leaving 
half the hole (the size of pivot or screw at /) in b it 
can be readily attached to any lever, so as to fulfil the 
conditions of being true with the pivot ; or since the 
whole of a circle will naturally be turned in making^, 
the whole of the hole may be left in it, forming the 
bearing for the pivot. 

Another form of reducing-lever is shown in Fig. 2. 
This is pivoted and connected to the cross-head, the 
same as that shown in Fig. I ; but the cord is attached 
to a piece e, so that a line drawn from pivot/* to the 
point of attachment shall be at right angles to the 
cord leading to the indicator when the lever a is verti- 
cal and the engine at mid-stroke. The direction of 
the cord to the indicator may be at any angle up or 
down, but must be in line with the swing of the lever. 

In Fig. 3 the lever a is slotted at the lower end, and 
works on a pin in the cross-head. The cord is attached 
directly to the lever or to a projecting screw, and must 
leave the lever at right angles to it when in a vertical 
position, and in line with its swing; hence with this 
reducing motion it is generally necessary to use a small 
guide-pulley represented at g. After leaving the guide- 
pulley the cord may lead in any direction whatever to 
the indicator. The distance from pivot f to the point 
at which the cord is attached will be the same in the 
last two examples of levers as the radius of b in the 
first example, and may be found in the same way. 

All the parts of these reducing motions are repre- 
sented as made of wood. If a permanent arrangement 



20 INDICATOR PRACTICE. 

is desired they may be made of metal. In any case 
the joints should be free from lost motion. 

A variety of modifications may be made to suit dif- 
ferent conditions. The lever may extend downward 
instead of upward, or horizontally to either side. 
More than one guide-pulley may be used: it is better, 
however, to use as short and direct cord as possible, 
and if practicable to avoid the use of guide-pulleys 
altogether; this is especially advisable at high speed. 

Generally, — particularly on short-stroke engines, — 
when the reducing motion is to be used regularly on 
one engine, or on engines of the same class, a standard 
for the upper pivot of the lever may be attached to 
some part of the bed so as to be put up and taken 
down quickly. 

Planning for attaching the indicator and getting the 
drum-motion should be simultaneously done. Some- 
times the indicator, by the exercise of a little fore- 
thought, may be arranged to greatly simplify the con- 
necting to the drum ; sometimes a particular arrange- 
ment of the drum-motion will permit the indicator to 
be much more advantageously set. Generally the 
whole matter is simple, but in special instances, where 
there is but little space to work in, considerable in- 
genuity will be required. Attention must be paid to 
the arrangement of levers and to the direction in 
which the cord is led, as has already been referred to. 
Reflection will show that if this is not done the mo- 
tion will not be correct. When the temptation is to 
lead the cord a little indirectly from the lever, the ef- 
fect of doing so may be better seen by, in imagination, 
going to the extreme in the same direction. And the 



DRUM MOTION. 21 

same is true of setting the lever so that it does not 
vibrate equally to each side, etc. A correct under- 
standing of what is wanted must first be had, then 
judgment used in obtaining it. The reduced motion 
by levers will hardly ever be absolutely correct, but 
when properly arranged the variation will be unim- 
portant. 

Other means than simple levers are sometimes em- 
ployed for giving motion to the paper-drum. Some- 
times a pantograph, so called, is used ; sometimes 
reducing- wheels. The writer has never found any- 
thing so satisfactory as one of the three arrangements 
shown in Figs. I, 2, and 3, preferably used without the 
guide-pulley ; hence others will not be described. 

It is perhaps needless to say that the reason why 
the use of a short direct cord is to be preferred is that 
the shorter the cord the less it will stretch, and guide- 
pulleys may cause slight irregularities, besides stretch- 
ing the cord more because of increased friction and 
inertia. 

LENGTH OF DIAGRAMS. 

It is advisable to take a fairly long diagram, because 
if all the motions are correct the longer the diagram 
the less the liability to error in measuring it. A long 
diagram is also better than a short one when taken for 
adjusting valves, because slight variations are repre- 
sented at correspondingly greater magnitude. On the 
other hand, and particularly at high speed, the attempt 
to get large diagrams will sometimes introduce errors 
of greater importance than those it is sought to avoid. 
On long-stroke engines diagrams may be taken as long 



22 INDICATOR PRACTICE. 

as five inches, bat four and one half inches is better 
practice. From this length as the extreme they may- 
be taken four inches, three inches, two inches, or even 
less — according to speed and other conditions. Judg- 
ment must t,e used in this respect. At high speed the 
inertia of the paper-drum becomes an important factor, 
and if the attempt is made to take a full-length dia- 
gram this will in some degree affect its truthfulness. 

BEST CORD TO USE. 

The best cord to use is of braided linen, about one 
twelfth inch in diameter. It should be well stretched 
before being used, by attaching one end to something 
overhead and hanging a weight on the other end, al- 
lowing it to remain in this condition not less than 
twenty-four hours (it should not be allowed to untwist 
in being stretched) ; then go over it with a piece of 
bees-wax and afterward with a piece of wood with a 
notch in it, keeping it well stretched at the time. When 
thus treated, it may be wrapped in paper and laid in 
the box for future use. It will be found not liable to 
stretch, and will not be readily affected by water or 
steam. So much wax should not be used as to make 
the cord stiff and unwieldy. 

If a steel hook or ring is used for connecting with 
the hook on the indicator it should be quite light, or it 
may cause the cord to " throw/' 



TAKING THE DIAGRAMS. 23 



CHAPTER V. 
TAKING THE DIAGRAMS. 

ADJUSTING THE LENGTH OF THE CORD. 

The indicator may be swung around one way or the 
other, and the piece carrying the guide-pulleys at the 
lower end of the drum may be moved so as to lead the 
cord fairly. After fastening the hook, or making a 
loop, so that the cord is presumably the right length, 
take hold of the end of one cord with each hand, 
letting one follow the motion of the reducing-lever, 
keeping the cord taut, and with the other pull the 
drum around from one stop to the other, observing if 
the cord needs lengthening or shortening to insure the 
drum travelling about as near to one as to the other. 
Having lengthened or shortened the cord, if necessary, 
hook the two cords together and note if the motion is 
smooth. 

ADJUSTING THE PAPER AND PENCIL. 

The paper should be so placed on the drum that the 
clips hold it stretched quite smoothly and evenly, 
otherwise the diagram will be distorted and worthless. 
Sharpen the pencil to a smooth fine point; a piece of 
fine sand-paper is best for this purpose. Adjust the 
pencil-stop so the pencil will bear no harder than just 
sufficient to make a plain mark: harder than this 



24 INDICATOR PRACTICE. 

creates unnecessary friction and makes the diagram 
untrue. 

Everything being in readiness, the pencil out of con- 
tact with the paper, open the indicator-cock and hook 
the cords together. At high speeds some little diffi- 
culty will be experienced in connecting the cords, but 
a little practice will overcome it. By this time the 
indicator-piston will have made a few strokes, and the 
indicator-cylinder will be warm ; then move the pencil 
up to the paper and hold it there while the engine 
makes a double stroke and the pencil traces the dia- 
gram. Swing the pencil away, close the cock, and 
immediately return the pencil and trace the atmospheric 
line ; then unhook the cords. 

This being the first diagram, it is important to know 
that the indicator is working properly. One precaution 
that may be taken to that end is to again open the 
cock, let the piston make a few strokes, then close it, 
and, bringing the pencil close to the paper, turn the 
drum by hand and observe if the pencil covers the 
atmospheric line just traced ; then note if a slight 
pressure up or down on the pencil-lever will cause the 
pencil to stand above or below the atmospheric line. 
The pencil at these tests should cover the atmospheric 
line : if it fails to do so, the pencil movement is not 
free in the joints, there is lost motion, or the piston is 
not free in the cylinder. The piston should be kept 
well oiled, and the freedom of the pencil movement 
should be tested before putting in the spring. 

Being sure that the indicator is working quite freely, 
as many diagrams as are desired may be taken, as fast 
as each one is removed from the drum such memo- 
randa as seem pertinent being made upon it. 



TAKING THE DIAGRAMS. 2$ 



PRINTED BLANKS. 



Printed blanks may be had from the printer at a 
trifling expense. They are convenient, always ready 
for use, and make it probable that data that will per- 
haps some time be valuable will be preserved. They 
should be, for an ordinary drum, about 3J X 7$ inches. 
Those used by the writer are printed as follows : 

Diagram taken by at 188 



From End of Engine. 

Built by - 

Diameter Stroke Clearance Revolutions Boiler-pressure . 

Vac. per gauge Air-pump diameter Stroke 

Tern, of Injection Discharge 

Diameter of steam-pipe Length 

Diameter of exhaust-pipe Length . 

Tern, of feed Valve gear 

Governor Position of throttle Vertical scale 

Remarks. 



26 INDICATOR PRACTICE. 



CHAPTER VI. 
READING THE DIAGRAM. 

ABSOLUTE INFORMATION CONVEYED BY THE FIGURE TRACED. 

HAVING taken the diagram, the next consideration 
is how to read it. The figures traced by the pencil 
will vary widely under the different conditions of dif- 
ferent engines from which the diagrams are taken, or 
from the same engine under different conditions; and 
it is necessary to know how to interpret these vari- 
ations — to reason back to the cause that produces the 
effect. The only absolute information the diagram 
conveys, whatever its form, is the pressure in the cylin- 
der of the engine. All the other information to be had 
from it comes through processes of reasoning. 

Knowing that the pencil will at all times stand at a 
height corresponding to the pressure in the cylinder, 
and that the length of the diagram will, on some scale, 
represent the stroke of the engine, it will be readily 
understood that if steam of full boiler-pressure was ad- 
mitted to the cylinder at the beginning of the stroke, 
and maintained to the end ; if then all the steam was 
instantly discharged and the piston returned against 
the pressure of the atmosphere if the engine is non- 
condensing, or against no pressure if condensing — the 
figure described by the indicator-pencil would be a rect- 
angle, the height of which would represent the pres- 



READING THE DIAGRAM. 



27 



sure of steam in the boiler, and the length the stroke 
of the piston. If it were possible it is not desirable 




£ 



that the construction of the engine should be such as 
to produce this diagram. 



Yet such a diagram would 



28 INDICATOR PRACTICE. 

represent some good features — better than are obtained 
in practice. But it would show a lack in one essential 
feature ; that of taking advantage of the expansive 
property of steam. 

NAMES OF THE DIFFERENT LINES OF THE DIAGRAM. 

Fig. 4 represents a diagram from a non-condensing 
automatic cut-off engine. A is the atmospheric line. 
This line, though traced by the pencil of the indicator, 
has no connection with the conditions existing in the 
cylinder of the engine. It is drawn, as previously ex- 
plained, when the indicator-cock is turned so as to 
close the communication between the indicator and 
engine cylinders, and with atmospheric pressure on 
both sides of the indicator-piston. It is of the first 
importance to establish this line correctly ; it is the 
neutral line of the diagram, and from it all pressures 
above and below it must be determined. 

Fis the line of perfect vacuum, or no pressure : this 
line is drawn by hand at a distance below A equal, by 
the scale of the spring, to the pressure of the atmos- 
phere. When this pressure is not known, it is at ordi- 
nary altitudes assumed to be 14.7 pounds per square 
inch. This is about the average pressure at the sea- 
level ; at high altitudes it is materially less. 

DE is the admission-line, so called because its begin- 
ning, D, represents the point in the stroke of the en- 
gine at which the steam-valve begins to a^mit steam 
to the cylinder.* 

*The terms '* steam-valves" and "exhaust-valves" are, for con- 
venience, used without reference to whether the engine has one or 
four valves. 






READING THE DIAGRAM. 29 

EF is the steam-line, considered as beginning at the 
point of positive change in direction of the admission- 
line, as at E, and terminating at the point of cut-off, F. 

The expansion-line, FG, is traced after admission of 
steam to the cylinder has ceased, the pressure falling 
by expansion while the piston is travelling a distance 
represented on the diagram by the distance horizon- 
tally from F to G. 

The exhaust-line begins with the opening of the ex- 
haust-valve at G, and continues to the end of the for- 
ward and beginning of the return stroke. 

HI is the line of counter-pressure, beginning with 
the return stroke and continuing to /", at which point 
the exhaust-valve is closed. 

The compression-line begins at / and continues to 
D, the pressure rising as the steam remaining in the 
cylinder is compressed into less volume, substantially 
as it fell with the increase of volume during expansion. 

This designation of lines is to a certain extent con- 
ventional, and is adopted more for convenience than 
for exactness of expression. The admission-line, for 
instance, might properly enough be considered as con- 
tinuing from the time of opening till that of closing of 
the steam-valve, and the exhaust-line from the open- 
ing till the closing of the exhaust-valve ; but they are 
more conveniently referred to when further divided, as 
noted. 

The beginning and termination of some of these 
lines are called points, and their continuation periods 
in the stroke of the piston. Thus F represents the 
point of cut-off and FG the period of expansion. 



30 INDICATOR PRACTICE. 

DATA NECESSARY AND USEFUL. 

The names of the lines of the diagram are the 
alphabet, as it were, by which it is read. As a further 
aid in comprehending it several things having reference 
to permanent and accidental conditions should be 
known. Those more particularly essential are noted 
on page 25. Diagrams are often practically worthless 
because so little is known about the conditions under 
which they were taken : hence the data should be 
made as complete as practicable. When this is done 
their study is pleasant and profitable, showing, by 
comparison, the effect of different construction and 
operation. 

THE USE OF THE INDICATOR FOR ADJUSTING VALVES. 

One of the uses of the indicator, and an important 
one, is in adjusting the valves of all classes of steam- 
engines. However carefully valves may be adjusted 
when the engine is not under steam, expansion, and 
perhaps some springing of parts, will cause derange- 
ment — sometimes serious — when the engine is work- 
ing. In many engines having automatic valve-gear 
derangement by wear of some of the parts is likely to 
bring about improper and expensive action ; in fact in 
any engine derangement will always occur by the 
wearing of parts. In all such cases the indicator is a 
ready means of locating the trouble. Builders do not 
consider their engines completed until the final adjust- 
ment of valves by the use of the indicator ; users can- 
not be assured that their engines are working economi- 
cally except by the regular use of this instrument. 



READING THE DIAGRAM. 



31 



LEAD. 

Suppose the indicator is applied to an engine, the 
result being a pair of diagrams similar to those repre- 
sented in Fig. 5. In Fig. 4 the admission-line is verti- 
cal, showing that the steam-valve opened sufficiently 
to admit steam to fill the clearance-space at about 
boiler-pressure before the piston began its stroke. In 
A, Fig. 5, the admission-line is inclined in the direction 




Fig. 5. 

of the stroke of the piston. We should infer that the 
valve began to admit steam just as the piston began its 
forward stroke, instead of, as is the more common 
practice, just before the termination of the return 
stroke. Just how far the piston has moved before full 
pressure is admitted may be readily determined. 
Measuring the distance at a it is •§■ inch, and the length 
of the diagram is 2-f inches ; \ inch is ^- part of 2-f 
inches, so the piston has made -^ part of its stroke up 
to the point of full admission. If the stroke is, say, 



32 INDICATOR PRACTICE. 

12 inches, the piston has moved |-f- inch up to this 
point. 

Generally prompt admission, as in Fig. 4, is favored 
by engineers, the argument being that the cylinder and 
piston having been cooled during exhaust the exposed 
surfaces should be heated as early in the stroke as 
practicable. On the other hand, it is reasoned by those 
who favor late admission, that, while the crank is at 
and near the dead-centre pressure against the piston 
will have no effect to turn the shaft, but on the con- 
trary will create friction on the pins and main journals, 
which tends towards preventing its turning ; for this 
reason they advise that the pressure in the cylinder be 
keot low at this time. 

There is reason in both these arguments. The 
writer does not believe there is much of either loss 
or gain in admission that is a trifle late,* and would 
always make it such as seems to bring about the best 
conditions otherwise. When the ports are small or 
when the clearance is large late admission may result 
in a low steam-line (low compared with boiler-pres- 
sure), which is a condition unfavorable to economy; in 
such cases the valve should have lead. In other cases 
it may or may not have lead, according as the engine 
runs smoother with or without it. 

Referring to B, Fig. 5, from the other end of the 

* These terms are used in accordance with the custom of speaking 
of lead as the extent of the opening of the steam valve, in the line of 
its travel, with the crank is on its dead-centre; early admission, such 
as results in an admission-line as in Fig. 4 ; lack of lead, no opening 
of steam-valve until the piston has commenced its forward stroke; 
and late admission, as in A, Fig. 5, the result of lack of lead. 



READING THE DIAGRAM. 



33 



cylinder, it will be seen that conditions contrary to 
those in A exist; that the steam-valve on this end 
opens considerably before the end of the return stroke. 
(By forward stroke, that stroke of the piston in which 
steam is admitted to the end of the cylinder under 
consideration is understood ; by return stroke, its 
stroke in the opposite direction.) The lead is exces- 
sive on this end. Equalizing the lead will make it 
about like that in Fig. 4 on both ends. If both dia- 
grams were like A, the eccentric should be advanced 
to bring this about ; if like B, it should be moved back 
to reduce the lead. 

EARLY AND LATE EXHAUST-CLOSURE. 

A, Fig. 6, shows too much compression. By early 
exhaust-closure the pressure behind the piston is in 




Fig. 6. 



creased, until before the completion of the return stroke 
it is higher than that in the steam-chest ; then when 



34 INDICATOR PRACTICE. 

the steam-valve opens the pressure falls, making a loop 
in the diagram. The remedy for this is to bring about 
later closure of the exhaust-valve. Modern practice 
largely favors, when practicable, an exhaust-closure 
that will compress the imprisoned steam to about two 
thirds as high as initial pressure. Fig. 4 shows com- 
pression to that extent, and is about right. 

The argument in favor of compression is, that it fills 
the clearance-space with steam that would otherwise 
be wasted, and thus effects a direct saving of steam, 
which is true to a certain extent ; also, that it tends to 
smooth running, which is equally true. There is al- 
ways some looseness in the main journals and connect- 
ing-rod boxes, and this if taken up suddenly, as it is 
when steam of high pressure is instantly brought to act 
on the piston, produces a jar or pound. If the ex- 
haust-valve is closed at the proper time in the stroke, 
the pressure on the exhaust side of the piston increases 
till it equals and then becomes greater than the pres- 
sure urging the piston along: this comes about so 
gradually that the tendency is to take up what lost 
motion there may be in the same gradual manner. 

Increasing compression will not always stop pound- 
ing in an engine; but when it is quite low, increasing 
it will generally have an effect that way. Some en- 
gines run satisfactorily, so far as jar is concerned, with 
little or no compression. To be of much service in 
bringing about smooth running, compression should 
be carried to a higher point than the pressure in the 
other end of the cylinder at the termination of the 
stroke. If we suppose the diagram from the other end 
of the cylinder to be a duplicate of that shown in Fig. 



READING THE DIAGRAM. 35 

4, then the pressure at the end of the compression-line, 
as at D, should be higher than at G. If the pressure 
is enough higher at D than at the end of expansion to 
have gradually overcome the forward pressure, and 
the momentum of the reciprocating parts, all will have 
been done that can be by compression to insure still 
running. To insure an arresting of tendency to mo- 
tion in one direction and a tendency to motion in the 
opposite direction of the reciprocating parts, the pres- 
sure, except in the case of low speed, must be materi- 
ally higher at D than at G. 

In B, Fig. 6, the exhaust-valve closes too late. There 
is no compression, showing that the exhaust is open 
until the end of the stroke. The exhaust-valve should 
be made to close earlier in B and later in A, 

EARLY EXHAUST-OPENING BACK-PRESSURE. 

Moderately early exhaust-opening, as represented at 
G y Fig. 4, gives time for the escape of steam before the 
piston begins its return stroke, and assists in keeping 
the back-pressure low. As the piston gets near the 
end of its stroke, pressure on it is nearly all, then en- 
tirely, spent in creating friction : so it is always advan- 
tageous in this respect to open the exhaust before the 
end of the stroke. It is very seldom that diagrams 
from stationary engines are seen which represent actual 
loss from too early exhaust-opening : very frequently 
diagrams that represent a loss of from one to five 
pounds in back-pressure from late exhaust are met 
with. The matter of exhaust opening and closure is 
only to a limited extent in the hands of the engineer, 
as it is largely controlled by the designs of the builder. 



36 INDICATOR PRACTICE. 

The engineer frequently finds himself obliged to com- 
promise as between too much tendency to pound and 
a loss from back-pressure. 

The back-pressure in a non-condensing engine, rep- 
resented by the distance apart of the atmospheric line 
and the line of counter pressure, varies with the con- 
struction of the engine, the speed at which it runs, and 
the adjustment of the valves, and to a considerable 
extent with the pressure in the cylinder at exhaust- 
opening. Sometimes it is as little as one-half pound 
— even less ; but two pounds is nearer an average. 
Excessive back-pressure may be caused by small ports, 
small exhaust-pipe, or tortuous passages. Late ex- 
haust-opening, as previously referred to, tends to in- 
crease back-pressure ; the presence of water in the 
cylinder has the same tendency. 

WAVY LINES — SERRATED LINES. 

The wavy lines of Fig. 7 result from natural causes — 
from high piston-speed, reaction of the spring, and 
momentum of the reciprocating parts of the indicator. 
When the waves are symmetrically rounded and not 
too intense — not much more so than in Fig. 7 — they do 
not materially affect the truth of the diagram. When 
the undulations are considerably more intense than in 
this figure, the remedy is to use a stronger spring, and 
sometimes to shorten the motion of the paper-drum. 

Serrated lines, as in Fig. 8, are evidence of undue 
friction in some of the parts of the indicator, and make 
the diagram worthless. Sometimes when the instru- 
ment is new the piston maybe a trifle tight — so much 



READING THE DIAGRAM. 



37 



so as to stick in the cylinder. The remedy is to attach 
the indicator to an engine (not connecting the drum- 
motion), and, keeping all parts well oiled, let it work 



Fig. 7. 




Fig. 8. 



for an hour or two. If the instrument is not new, it 
requires cleaning and oiling, and an examination to see 
that there is no derangement of parts. 



38' INDICATOR PRACTICE, 



CHAPTER VII. 
HEAT— THE EXPANSION OF STEAM. 

HEAT. 

We speak of the consumption of steam by the 
steam-engine, but behind this is the well-known fact 
that a certain amount of steam represents a definite 
amount of heat. Heat is converted into work, — mo- 
tion against resistance, — steam being the medium. 
This heat appears in tangible form in the furnace: a 
portion of it is transferred to the water in the boiler, 
some of it escapes through the chimney, and some 
of it warms the surrounding air. Of the heat that 
is utilized in making steam, some is lost before it 
reaches the cylinder, some by radiation from the 
cylinder, and some is transformed into the work of 
moving the piston against the resistance it encounters. 
But the greater part of it finds its way out of the 
cylinder with the exhaust-steam, into the condenser or 
the atmosphere. It is not possible, in the light of pres- 
ent knowledge, to realize as motion in the machinery 
more than a small percentage of the heat that appears 
in the furnace ; economy in steam-engineering consists 
in part in making this percentage as large as prac- 
ticable. 

HEAT OF COMBUSTION OF COAL. 

The heat of combustion of one pound of coal of 
good quality is 14,500 heat-units, each equivalent to 



HEAT— THE EXPANSION OF STEAM. 39 

772 units of work. If then the heat of combustion of 
one pound of coal could be employed in raising a 
weight of one pound, it will raise it a distance of 
14,500 X 772 = 11,194,000 feet, or more than 2000 
miles ! We may very readily see what proportion of 
this work is done in the steam-engine by the heat 
from one pound of coal burned in the furnace. Sup- 
pose this pound weight to be raised to the height 
named in one hour. A horse-power is 33,000 pounds 
raised one foot high in one minute, or 33,000 X 60 = 
1,980,000 feet in one hour — 1,980,000 foot-pounds. 
Then 11,194,000 -f- 1,980,000 = 5.65 horse-power ex- 
erted for one hour will raise this weight. It is an 
exceptionally good steam-engine that will develop a 
horse-power per hour with the consumption of 1.75 
pounds of coal ; and with such an engine to do work 
equal to raising this one pound weight 11,194,000 feet 
would require 5.65 X 1-75 = 9-88 pounds of coal, about 
10 per cent of the heat of combustion being made to 
do useful work in the cylinder. 

BOILER DUTY. 

When coal is burned by natural draught in the 
furnace of a boiler from 18 to 24 pounds of air must 
be admitted for each pound of coal burned. To 
maintain the necessary draught, the gases must enter 
the flue at a temperature of from 400 to 6oo°, carry- 
ing with them considerable heat. The heat passing 
off through the chimney, lost by radiation from fur- 
nace, etc., and by unconsumed fuel, may be taken 
under favorable conditions to be 30 per cent of the 
heat of coal: it is seldom less than this, and frequently 



4-0 INDICATOR PRACTICE. 

much more. The heat transferred ' to the water is 
then about 70 per cent, or 14,500 X .70 = 10,150 heat 
units per pound of coal. 

THE CONVERSION OF WATER INTO STEAM. 

Assume one pound of water at a temperature of 40 
to be converted into steam of the pressure of the at- 
mosphere. To bring this water to a temperature of 
212 , the boiling-point, there must be added 212 — 40 
= 172 units of heat.* If the heat is continued and 
the steam allowed to pass freely into the atmosphere 
965.7 more units of heat must be added, making 
altogether 1 137.7 heat -units imparted to the pound 
of water. These 965.7 heat-units are the latent heat 
of steam at atmospheric pressure. The latent heat of 
steam at other pressure may be found from Table II., 
as explained in the text immediately following the 
table. 

If steam of 100 pounds pressure is to be generated 
in a boiler, we find from the table that it will contain 
1213.8 heat-units per pound. If the water is heated, 
as in a feed-water heater, to 160 , there must be im- 
parted to it 1213.8 — 160 = 1053.8 heat-units. Then 
the 10,150 heat-units mentioned in a preceding para- 
graph would evaporate 10,150 -4- 1053.8 = 9.63 pounds 
of water. This result is considerably above the average. 

*This is not strictly correct, because as the temperature of the 
water is increased above 40 the addition of a unit of heat will raise 
its temperature slightly more than one degree; but the increase is so 
slight, amounting altogether to less than one heat unit from 40 to 
212 , it need not be considered. For all ordinary purposes we may 
calculate that if we add one heat-unit to a pound of water below 212 
it will increase its temperature one degree. 



HEAT— THE EXPANSION OF STEAM. 41 

THE EXPANSION OF STEAM MARIOTTE's LAW. 

Steam expanding in the cylinder of an engine doing 
work follows with reasonable exactness the law of 
gases known as Mariotte's law, the pressure varying 
inversely as the volume. According to this, if steam 
of 80 pounds absolute pressure per square inch is ad- 
mitted to the cylinder of a steam-engine for one half 
the stroke, neglecting clearance for the time being, the 
pressure at the end of the stroke will be 40 pounds; 
or if the steam follows one-quarter stroke, the pressure 
at the end of the stroke will be 20 pounds ; etc. In 
the first-named instance there is a pressure against the 
piston of 80 pounds, absolute, per square inch for one 
half the stroke, and for the other half the pressure 
varies from 80 pounds to 40 pounds. In the second 
instance the pressure is 80 pounds for one quarter of 
the stroke, and for the remaining three quarters it 
varies from 80 pounds to 20 pounds. What we want 
to know is the mean pressure for the entire stroke. 
This may be calculated very readily by the aid of 
Table III. Such calculations are useful in estimating 
the probable power that may be had from an engine 
of given dimensions and at different ratios of expan- 
sion. 

Suppose it is required to find the mean pressure of 
steam of 100 pounds absolute pressure, cut-off at 6 
inches in a cylinder, the stroke of the piston of which 
is 24 inches : 24 -f- 6 = 4, the ratio of expansion. 
This (4) will be found in Table III., under the heading 
Number, and opposite it is 2,386. Multiply this by 
the steam-pressure 2.386 X ICO = 238.6. Divide this 



42 INDICATOR PRACTICE. 

by the ratio of expansion, 238.6 -f- 4 = 59.65, the mean 
pressure in pounds per square inch of steam of ICO 
pounds absolute pressure cut off at one-quarter stroke. 

RULE FOR FINDING THE MEAN PRESSURE OF EXPANDING 

STEAM. 

From the foregoing example the following may be 
deduced : To find the mean pressure of expanding 
steam, multiply the hyperbolic logarithm -f- x of the 
number representing the ratio of expansion by the 
absolute pressure at cut-off, and divide the product by 
the ratio of expansion. 

To find the ratio of expansion, divide the stroke in 
inches by the number of inches of the stroke com- 
pleted when steam is cut off. 

To be exact in calculating the mean pressure from 
the table, the clearance must be taken into account. 
Thus, if in the example the clearance had been such 
as in effect to add three quarters of an inch to the 
length of cylinder on each end, this must be added to 
the stroke of piston, and also to the distance the 
piston has moved before cut-off: 24 -f- .75 = 24.75, 
6 -f- .75 = 6.75, and 24.75 -f- 6.75 = 3.6, the ratio of 
expansion. From Table III. the hyperbolic logarithm 
-f- 1 of the number 3.6 is 2.281, which multiplied by 
100 is 228.1, and this divided by 3.6, equals 63.36 in- 
stead of 59.65, as before. 

As calculations of this kind are made for approxi- 
mate results only, it is not generally necessary to take 
note of clearance, unless it is large, or unless the cal- 
culation is made for quite early cut-off; it may be as- 
sumed that what will be gained by clearance will be 



HEAT— THE EXPANSION OF STEAM. 43 

lost by failure to realize boiler-pressure in the cylinder, 
and by fall of pressure before cut-off. 

From the mean pressure as found in the preceding 
example not less than 16 pounds absolute back-pres- 
sure should be deducted for a non-condensing engine, 
and not less than 3 pounds for a condensing engine. 
If there is much compression, a further deduction must 
be made, according to conditions. 

ECONOMY OF EXPANSION. 

As will be seen by reference to Table II., the weight 
of a given volume of steam varies nearly as its pres- 
sure; that is, a cubic foot of steam at 40 pounds pres- 
sure weighs approximately twice as much as the same 
volume at 20 pounds pressure. As the weight of 
steam represents the weight of water that must be 
evaporated to produce it, the lower the terminal pres- 
sure at exhaust-opening in a given cylinder the less 
the amount of water exhausted as steam. The mean 
effective pressure is a measure of the work done in the 
cylinder by the steam ; hence it is plain that economy 
in the use of steam in a steam-engine consists in part 
in making the mean effective pressure large and the 
pressure at exhaust -opening small — getting a good 
deal of work and exhausting a small quantity of steam. 
This is done by working steam expansively, by cutting 
off the supply when the piston has made a part only 
of its stroke, and then getting work from the expand- 
ing steam to the end of the stroke. In the preceding 
example it was seen that with steam of 100 pounds 
absolute pressure, cut off at one quarter stroke, the 
mean pressure will be about 60 pounds. This is ob- 



44 INDICATOR PRACTICE. 

tained by filling the cylinder only one quarter full of 
steam. If the entire cylinder had been filled the mean 
pressure would have been only ioo pounds. This in- 
dicates the direction in which saving is effected, but 
not the degree of saving. In practice, condensation in 
the cylinder, and other causes, prevent the full theo- 
retical gain from expansion being realized. But the 
gain is an important one. 

The foregoing will naturally lead to the conclusion 
that in considering diagrams from cut-off engines we 
shall expect in a good one to find the initial pres- 
sure high compared with the boiler-pressure, the steam- 
line reasonably straight and cut - off sharp, because 
these all tend to bring about high mean effective and 
low terminal pressure ; also, that whatever tends to 
make the terminal pressure higher than it should be 
represents waste of steam. 

THE ECONOMY OF HIGH PRESSURE. 

A brief consideration of the subject will show why 
the use of high-pressure steam is economical. Taking 
for example an engine working without expansion, 
and for simplicity assume that there is no clearance. 
Assume the engine to be working non-condensing, and 
the total back-pressure to be 15 pounds — T 3 ^ pounds 
above atmosphere. If in this cylinder steam of 20 
pounds absolute pressure is used, the mean effective 
pressure is 20 — 15 = 5 pounds. Suppose the cylinder 
to have a capacity of one cubic foot. We are using, then, 
at each single stroke of the piston one cubic foot of 
steam of a pressure of 20 pounds. In Table II. the 
weight of a cubic foot of steam of this pressure is found 



1 



HEAT— THE EXPANSION OF STEAM. 45 

to be .0511 pound, and the heat-units per pound 
1 183.5 > hence the cubic foot of steam from which the 
mean effective pressure of 5 pounds has been obtained 
contained 1 183.5 X .0511 =60.5 heat-units. 

Instead of steam of 20 pounds pressure, let steam of 
100 pounds be used. The mean effective pressure is 
100— 15 = 85 pounds. The weight of a cubic foot of 
steam of 100 pounds pressure is .2330 pound, and one 
pound contains 1213.8 heat-units. Then, as before, 
1213.8 X .2330= 282.8 heat-units used. 

In the first instance, 60.5 -f- 5 = 12. 1 heat-units are 
required for each pound mean effective pressure ; in 
the second, 282.8 -=- 85 = 3.3. 

The reason for this wide difference in either instance 
is that the greater part of the total heat of the steam is 
still in it at the pressure of exhaust (15 pounds), and 
this is all thrown away. It is only from the heat that 
is added above exhaust pressure that any can be con- 
verted into useful work. As the pressure is increased, 
a greater per-cent of the total heat is, as will be 
readily understood, available. If the piston would just 
move without any effect from the steam, we might go 
on throwing away a cylinderful at 15 pounds pressure 
at each half-stroke of the piston, without doing any 
work whatever. 

A clear conception should be had of the fact just 
referred to, that a large proportion of the heat that 
goes into the steam used in a steam-engine is required 
to raise it to the pressure at exhaust, at which pressure 
no work can be done with it. 

The most satisfactory illustration of the economy of 
the use of high-pressure steam in a cut-off engine is by 



4 6 



INDICATOR PRACTICE. 



means of the diagram. Fig. 9 shows it graphically. 
This is, so far as bounded by the full lines, an actual 
diagram ; above it has been plotted the shaded part 




precisely as if the whole was a diagram taken at higher 
steam-pressure. The terminal pressure at t — that is, 
the pressure of the steam when we are through using 






HEAT— THE EXPANSION OF STEAM. 47 

it, — is not changed : hence we conclude that, so far as we 
can judge by the diagram, the work represented by the 
shaded portion could be done for nothing.* 

This subject is an important one: further reference 
to it will be found under the head of Steam-Engine 
Economy. 

* This is on the assumption that steam expands as represented in 
Chap. VII. If the result were worked out from Table II. it would be 
slightly different. But we do not know with certainty that it would 
be any nearer correct. For all practical purposes this presentation 
may be accepted, and in all consideration of diagrams that follow 
steam will be supposed to expand according to Mariotte's law. 



48 INDICATOR PRACTICE. 



CHAPTER VIII. 
COMPUTING THE HORSE-POWER. 

FINDING THE MEAN EFFECTIVE PRESSURE. 

FOR measuring from the diagram the mean effec- 
tive pressure, we may consider that the upper line — 
that is, all the inclosing lines of the figure that are 
traced while the piston is moving ahead — represents 
the pressure moving it, and that the opposing force is 
represented by the lower line traced while the piston 
is returning. A little reflection will show that the 
opposing force is actually represented by the lower 
line of a diagram simultaneously taken from the other 
end of the cylinder, but no error will arise in the pro- 
cess of finding the mean effective pressure by consider- 
ing the diagram from each end complete in itself. 
What we want is to measure the mean or average dis- 
tance apart of the upper and lower line of the diagram 
by the scale of the spring used : this will be the mean 
effective pressure — a factor in calculating the indicated 
horse-power. This is all that is required, except where 
expansion is carried so far that the expansion-line 
crosses the line of counter-pressure, or when compres- 
sion is carried to such an extent that a loop is formed 
at the termination of the return and beginning of the 
forward stroke. An instance of the kind first men- 
tioned — which is only likely to be met with in the case 






COMPUTING THE HORSE-POWER. 



49 



of a non-condensing engine cutting off short, as when 
lightly loaded — is represented in Fig. u, page 50; the 







second mentioned, of still rarer occurrence, is repre- 
sented in Fig. 6, page 33. 

The amount of work done on one side of the piston 
may differ materially from that done on the other 
4 



5o 



INDICATOR PRACTICE, 



side, and almost invariably does differ to some extent. 
For this reason, in finding the horse-power developed, 
it is necessary to measure diagrams from both ends of 




I 









the cylinder, when the average mean effective pressure 
of the two will be that required. 

Altogether, the most accurate and expeditious way 



COMPUTING THE HORSE-POWER. 5 1 

to measure the mean effective pressure represented by 
the diagram is by means of the planimeter, or averag- 
ing instrument ; but as such an instrument is not al- 
ways at hand, it may by careful working be very accu- 
rately done by dividing the diagram into a number of 
equal parts, say ten, as in Fig. 10, measuring the height 
of each division, adding these measurements together, 
and dividing the sum by the number of divisions. The 
only reason for making the number of divisions 10 is 
for convenience ; some prefer to make the number 
20, as tending to greater accuracy. The height of 
each division can be measured by a scale of pounds, 
the measurements added together and divided by 10, 
the result appearing in pounds ; or the measurements 
can be made by a scale of inches, the sum multiplied 
by the scale of the spring, and divided by 10, giving 
the result as before. As tending to greater accuracy, 
however, it is advisable to make the measurements 
continuous. For this purpose a strip of paper is used, 
which is carried from one division to another, the 
measure of each being pricked or marked beyond the 
preceding one, so that the distance from the end of the 
strip to the last mark will represent the sum of the 10 
measurements. 

In Fig. 10 this distance is 7.075 inches, the number 
of divisions 10, and the scale of the indicator-spring 
40 ; hence the mean effective pressure is 

7.075 X 40 , 

- — — = 28.3 pounds. 



52 INDICATOR PXAC7TCE. 



THE HORSE-POWER. 



The data required to find the indicated horse-power 
from a pair of diagrams are : The diameter of cylinder, 
stroke of piston, diameter of piston-rod, revolutions 
per minute, and scale of indicator-spring. In this in- 
stance the diameter of cylinder is 18.3 inches, stroke 
of piston 42 inches, diameter of piston-rod 3-J inches, 
revolutions per minute 72, and the scale of spring 1" = 
40 pounds. The mean net area of the cylinder (the 
total area less one half the area of piston-rod) is 259.18 
inches, and the piston-speed 504 feet per minute ; so 
that if the mean effective pressure of the diagram from 
the other end is the same as this, the indicated horse- 
power is 

259.18 X 28.3 X 504 



33,000 



= 112. 



Fig. 1 1 represents a case in which the pressure falls, 
by expansion, below the line of counter-pressure, cross- 
ing the latter at O, from which point to the end of the 
stroke it is plain that the pressure urging the piston 
forward is less than that resisting its progress. To get 
the mean effective pressure in such an instance, it is 
evident that the resistance indicated by the part M of 
the diagram must be deducted from the forward pres- 
sure indicated by the part N. This is conveniently 
done by measuring the combined height of the 4 
divisions included in N, similarly measuring the 6 
divisions of M f and subtracting the latter from the 
former. The combined height of the 4 divisions of 
N is 2f ", and of the 6 divisions of M \ n \ then 2|" — ■$" 






COMPUTING THE HORSE-POWER* 53 

= if ", which multiplied by 40 and divided by 10 gives 
a mean effective pressure of 7 pounds. 



PRECAUTIONS IN MEASURING THE DIAGRAMS. 

It should not be inferred that measuring the divi- 
sions of the diagram at their centres, as on the broken 
lines, will always be correct. It would be more nearly 
true to say that it will never be correct. It is the 
mean height of each division that is required, and the 
eye will generally determine whether this will result 
from measuring at the centre. In Fig. 10, measuring 
the height of the 10 divisions on the centre (broken) 
lines will give a mean effective pressure of 28.81 
pounds, or about \ pound too much ; and in Fig. 1 1 
it will give 6.5 pounds, an amount too small by more 
than 7 per cent. Why this is so will be better under- 
stood by an examination of the first and second divi- 
sions of Fig. 11, in each of which it is evident that the 
parts r f that ought to be measured, but are not in- 
cluded in a measurement on the centre line, are not 
equal with the parts r that are measured, but ought 
not to be. An examination of other divisions of both 
Figs. 10 and 11 will afford additional evidence that the 
practice of drawing the centre lines only and taking 
their measurements as conclusive is likely — almost 
certain — to lead to error. By drawing the boundary 
lines as well as the centre line of each division, then 
when any doubt exists, drawing the short horizontal 
lines (as near r, r'\ the spaces r, r' can be compared 
by the eye, after a little practice, with great exactness. 
Additional short horizontal lines can be drawn above 



54 INDICATOR PRACTICE. 

or below these to indicate the point to which to meas- 
ure to equalize the spaces, or where the case presents 
difficulties a division can be subdivided any number of 
times, and the height averaged in a way similar to that 
in which the height of the diagram is averaged. 

HORSE-POWER FOR ONE POUND MEAN EFFECTIVE PRESSURE. 

When a number of diagrams are to be calculated, the 
horse-power for one pound mean effective pressure 
may be computed, and this multiplied by the mean 
effective pressure of the different diagrams will give 
the horse-power of each. It is simply a shorter way 
to deal with several diagrams. Thus in the preceding 
instance the horse-power for one pound pressure would 
be 

259.18 x 1 x 504 



33,000 



= 3-9 6 > 



which multiplied by the mean effective pressure — 3.96 
X 28.3 == 212 — gives the horse -power the same as 
before. 






THE THEORETICAL CURVE. 55 



CHAPTER IX. 
THE THEORETICAL CURVE. 

REASONS FOR ESTABLISHING IT. 

If there were neither loss nor gain of heat by the 
steam in the cylinder of a steam-engine, nor leakage 
of the piston or valves, or other disturbing causes, the 
expansion-curve that would be traced by the indicator 
could be predetermined very nearly. But because 
there is a loss of heat, and because the piston and 
valves are in practice never absolutely tight, the ex- 
pansion-curve departs in a degree, greater or less, from 
the curve that would be established from theoretical 
considerations alone. For the purpose of determining 
the extent of this departure the theoretical curve is 
drawn upon the diagram and compared with the actual 
expansion-curve. The curve most commonly employed 
for this purpose is that of the hyperbola — the Mariotte 
curve. From what was said in Chapter VII. it will be 
understood that this curve is not the one that would 
be traced by the indicator under absolutely perfect 
conditions in the cylinder of the engine, but it is near 
enough so for all practical purposes, and its close ap- 
proximation by the diagram is, to a certain extent, 
evidence of good practice and conditions. But, as 
will be explained further on, this should not be blindly 
taken as being so, as it may indicate quite the reverse 



56 



INDICATOR PRACTICE. 



of good conditions. To state it in another way, when 
the actual and theoretical curves are found to agree 




< 

u 

C/3 



& 






substantially, it is strong presumptive evidence of good 
conditions. 

It is only necessary for the establishment of this 



THE THEORETICAL CURVE. 57 

curve to consider that the pressure of steam varies in- 
versely as its volume, or the space it occupies, from 
which consideration any desired number of points in 
the curve can be readily determined. Since all pres- 
sure must be measured from vacuum, and the clear- 
ance must be considered, the line of vacuum, F(Fig. 12), 
and the clearance line, C, are laid off, the former at a 
distance below the atmospheric line representing by 
the scale of the indicator-spring 14.7 pounds, and the 
latter at a distance, /i, from the beginning of the dia- 
gram, representing the added length of the cylinder 
that would equal the capacity of the clearance-space 
on one end. Suppose, as in the present instance, the 
clearance-space (which must include all the space that 
will be occupied by steam with the piston at the end 
of the stroke) is found to equal 4 per cent of the 
piston - displacement, which is represented by the 
length of the diagram ; the distance, k, will then be 4 
per cent of that length. 

There are different ways of establishing points in this 
curve, one of which is as follows : Draw on the dia- 
gram vertical lines, starting from the clearance-line, an 
equal distance apart, and number them as shown. In 
spacing these lines it is not necessary to pay any at- 
tention to coming out even at the end of the diagram ; 
one or more lines, as 16, may be quite beyond the 
diagram. Generally speaking, the more numerous the 
lines the more easily and accurately the curve may be 
drawn, but beyond this the number of lines is quite 
immaterial. 



58 INDICATOR PRACTICE. 



POINTS FROM WHICH TO DRAW THE THEORETICAL CURVE. 

The theoretical curve may be drawn from any point 
in the real curve, the only precaution necessary being 
to select a point at which it is known that the steam 
and exhaust valves are closed. Generally it is better 
to draw the curve from a point representing a piston 
position either just before the exhaust-valve opens, or 
just after the steam-valve has closed. In Fig. 12 the 
curve is drawn in broken lines from both these points. 
Selecting some point, as where the 14 line crosses the 
real expansion-curve, measure the pressure from vacuum 
up to this point. The scale of the spring is 40, and the 
pressure is 18 pounds. The number of volumes is, ac- 
cording to the unit adopted and represented by the dis- 
tance apart of the vertical lines, 14; hence to find the 
pressure on any other line, multiply this pressure by 
the number of the line, and divide the product by the 
number of the line upon which it is desired to deter- 
mine the pressure. Thus 18 X 14 = 252, which, divided 
by 5, equals 50.4 pounds, the pressure to be set off on 
line 5. By setting off the pressures on all the lines 
and connecting the points, as shown, the curve is es- 
tablished. 

Sometimes, near the point of cut-off, it will be found 
difficult to connect the points satisfactorily. When 
this is the case, another line, as 3^, may be drawn, and 
another point in the curve set off. In drawing the 
curve from the intersection of line 3, the same general 
plan is to be pursued ; that is, multiply the pressure on 
that line by 3, and divide by the numbers of the other 
lines to find the pressures on them. 



THE THEORETICAL CURVE. 59 

It will be understood that it is not necessary that a 
scale of pounds be used at all; or, if it be, it need not 
necessarily be the scale of the spring, as all that need 
be considered is that the product of the distance hori- 
zontally from C and the height from the vacuum-line 
V oi all points or parts of the curve are equal. Thus, 
if at a distance of 2 inches from C the pressure is 50 
pounds, at 3 inches it will be 

2 X 50 - - 

— - — = 33i pounds 

(2 X 50 = 100, and 3 X 33i = 100). 

It is of course necessary to establish the vacuum- 
line by the scale of the spring used in taking the dia- 
gram, but this may be done by dividing 14.7 (or any 
number of pounds corresponding to the observed pres- 
sure of the atmosphere) by the scale of the spring : the 
quotient will be in inches. In the present instance the 
distance of this line below the atmospheric line is 14.7 
-T- 40 = .3675" — a little less than -f inch. Having 
established the vacuum-line, any scale of equal parts 
may be used in setting off the points in the curve. 

If it is desired to show graphically how much higher 
the pressure is at the end of the stroke than it should 
be, the curve drawn as from the intersection of line 3 
will accomplish the purpose. But if it is desired to 
show how much more work might have been done with 
the steam accounted for by the indicator at the end of 
the stroke, then the curve should be drawn as from the 
intersection of line 14. In this instance, if the steam- 
line is continued till it cuts the upper curve, the space 



6o 



INDICATOR PRACTICE. 



O inclosed above the actual curve will represent this 
work. 

In selecting a point near cut-off from which to draw 




C/) 

I 






the expansion-curve it should be concluded that steam 
is not cut off until the flexure of the curve changes. 



THE THEORETICAL CURVE. 6 1 

Thus in diagram 14, for instance, the rounded corner 
near cut-off is occasioned by the contraction of the 
port-area while the valve is closing. At 5 the flexure 
or direction of the curve changes from concave up- 
ward to concave downward : we conclude that steam 
continued to enter the cylinder until this point in the 
stroke. In diagrams from engines in which the valve- 
motion closes the steam-port slowly the cut-off will be 
found at a point much later in the stroke than we 
might conclude from a casual inspection, and after a 
very material fall of pressure. Diagrams from loco- 
motive-engines at high speed show this peculiarity in 
a marked degree. 

GEOMETRICAL METHOD OF FINDING POINTS IN THE THEO- 
RETICAL CURVE. 

The following method of locating points in the theo- 
retical curve will doubtless be preferred by many to 
the preceding one : In Fig. 13 select any point, as/, in 
the actual curve, and from this point draw a vertical 
line to J on line B. The line B may be, as it is here, 
the line of boiler-pressure ; but this is not material : it 
may be drawn at any convenient height near the top 
of the diagram. From J draw the diagonal to K, K 
being the intersection of the vacuum and clearance 
lines, and from / draw I L parallel with the atmos- 
pheric line and at right angles to I J. From Z, the 
point of intersection of the diagonal JK and the 
horizontal line IL, draw the vertical line LM. The 
point M is the theoretical point of cut-off, and LM the 
cut-off line. Fix upon any number of points, 1, 2, 3, 
etc., on line B, and from these points draw diagonals 



62 INDICATOR PRACTICE, 

to K. From the intersection of these diagonals with 
LM draw horizontal lines, and from i, 2, 3, etc., verti- 
cal lines. Where these lines meet will be points in 
the theoretical curve. 

LOCATING THE CLEARANCE-LINE ON THE DIAGRAM. 

The clearance-space — such part of it as is embraced 
in the ports — is from its irregularity difficult of meas- 
urement. If the valve is blocked against the face, the 
engine placed on the dead-centre, and the clearance- 
space filled with water, the quantity being carefully 
weighed, the space it occupies will be known. Water 
at a temperature of 6o° will occupy a space of 27.7 
cubic inches per pound. Say that 6^ pounds are re- 
quired to fill the clearance-space in a i6 // X32 // cylinder, 
the cubic inches of space occupied by the water will 
be 27.7 X 6.5 = 180.05 cubic inches. The area of a 
16" cylinder is 201.068 inches, and the space swept 
through by the piston in a single stroke is 201.068 X 
32 = 6434.176 cubic inches; the clearance is 180.05 -f- 
6434.176 = .028 of the displacement. If the diagram 
is 4i inches long the distance h, Fig. 12, will be 4.25 X 
.028 = .119 inch. 

PROFESSOR SWEET'S PLAN FOR MEASURING CLEARANCE. 

The following remarkably simple plan for determin- 
ing clearance was communicated to the American Ma- 
chinist by Professor John E. Sweet. He says: "See 
that the piston and valves are made tight, and the 
valves disconnected ; arrange to fill the clearance-space 
with water through the indicator- holes, or through 



THE THEORETICAL CURVE. 



63 







64 INDICATOR PRACTICE. 

holes drilled for the purpose. Turn the engine on the 
dead-centre ; make marks on the cross-head and guides ; 
weigh a pail of water, and from it fill the clearance- 
space. Weigh the remaining water so as to determine 
how much is used. Then weigh out exactly the same 
amount of water [as is used], turn the engine off the 
centre, pour in the second charge of water, and turn 
the engine back till the water comes to the same point 
that it did in the first instance. Make another mark 
on the cross-head and guide, and the distance between 
these marks is exactly what you really wish to know ; 
that is, it is just what piston-travel equals the clear- 
ance. ... If it takes 1 pound of water to fill this 
space and to admit another pound, the piston must be 
moved 1 inch : then the clearance bears the same rela- 
tion to the capacity of the cylinder as 1 inch bears to 
the stroke of the piston. Thus, under these circum- 
stances, in an engine of 10 inches stroke, it would be 
said to have 10 per cent clearance.'' 

It may be added that, considering the length of the 
indicator-diagram as representing the stroke of the pis- 
ton drawn to a scale, it is only necessary to lay off this 
1 inch (or whatever the distance may be) on the same 
scale to establish the clearance-line on the diagram. 

It was remarked near the beginning of this chapter 
that it was evidence of good conditions when the theo- 
retical and actual expansion curves were found to agree, 
or very nearly so. Fig. \2\ shows reasonable compli- 
ance in this respect — in fact much better than the 
average; such as might be expected from a cylinder 
not much less than 16 inches diameter, working with 
piston and valves tight. 



MEASURING THE STEAM EXHAUSTED. 6$ 



CHAPTER X. 

MEASURING FROM THE DIAGRAM THE 
STEAM EXHAUSTED. 

STEAM EXHAUSTED PER HOUR. 

The amount of steam in the cylinder at any point in 
the stroke can be measured from the diagram, but un- 
fortunately the water present that entered the cylinder 
as steam cannot be so measured. For this reason the 
steam actually entering the cylinder cannot be deter- 
mined by the use of the indicator, but measuring that 
accounted for by the indicator we know that a less 
quantity could not have been used; in fact, we know 
that more — sometimes much more — is used. In meas^ 
uring the steam accounted for by the indicator it is 
generally advisable to select some point in the stroke 
just previous to the opening of the exhaust-valve, 
when the displacement of the piston in cubic feet up 
to that point, phis the clearance-space, multiplied by 
the weight of a cubic foot of steam of the pressure at 
the point selected, will give the weight of steam pres- 
ent. From this must be deducted the steam saved by 
the closing of the exhaust-valve before the end of the 
stroke, the remainder being the steam expended. In- 
stead of determining the steam used per stroke, it is 
better to calculate the amount used per hour. In Fig. 
14, which represents a diagram from an engine with a 
10" X 18" cylinder at 100 revolutions, 30 spring, a con- 
venient plan is represented. The lines, x, y, are drawn 



66 



INDICATOR PRACTICE. 



at a distance equal to the clearance-space from each 
end of the diagram. Measuring the pressure (from 
vacuum) on line y y it is found to be 27.5 pounds; and 
since j/ is at a distance from the end of the diagram 
equal to the clearance-space, it follows that the space 
occupied by steam at this point in the stroke is just 




Fig. 14— Scale 30. 

equal to the piston-displacement for a single stroke. 
The mean net area of the piston is, say, 77 inches, so 
the displacement is 77 X 18 = 1386 inches. The num- 
ber of single strokes per minute is 200, and per hour 
200 X 60 = 12,000; hence the displacement of the 
piston per hour is 



MEASURING THE STEAM EXHAUSTED. 6? 

12,000 x 1386 . 
Yj-28 = 9 62 5 

cubic feet. 

The weight of a cubic foot of steam at a pressure of 
27.5 is, according to Table II., .0695 pound (found by- 
adding the weight at 27 and at 28 pounds together, and 
dividing by 2) : so the weight of steam per hour in the 
cylinder at this point in the stroke is 9625 X .0695 = 
668.93 pounds. 

The process so far should be clearly understood : 
hence the repetition that, by measuring the pressure at 
y, distance from that end of the diagram just equal to 
the clearance-space C, the volume at that point (y) will 
be just equal to the piston - displacement ; we have 
added the clearance at C> but have cut off an equal 
distance at y. 

This 668.93 pounds is the weight of the steam per 
hour in the cylinder, as found by calculating it at some 
convenient point, y, on the expansion-curve. And 
this would be the weight of the steam exhausted per 
hour were it not for the fact that it is not exhausted 
down to vacuum, from which the pressure is cal- 
culated. Some of it is saved in the clearance-space 
upon the return of the piston, and this amount is in- 
creased by the exhaust-valve closing before the end of 
the return stroke. Line x is at a distance equal to 
the clearance from the end of the diagram, and the 
clearance is 7 per cent of the piston-displacement : 
hence if we calculate the steam saved per hour from 
the point where x crosses the compression-curve the 
volume will be just 14 per cent of the piston-displace- 
ment — that is, 9625 X .14 = 1347.5 cubic feet per hour. 



68 INDICATOR PRACTICE. 

The pressure of the steam saved, measured from va- 
cuum up to where x crosses the compression-curve, is 
22 pounds, and from Table II. the weight of a cubic 
foot of steam at that pressure is .0561 pound : hence the 
steam saved per hour is 1347.5 X .0561 = 75.59 pounds. 
The steam, then, actually exhausted is 668.93 — 75.59 
= 593.34 pounds per hour. 

The mean effective pressure is 29.6 pounds, and the 
piston-speed 300 feet per minute ; the indicated horse- 
power is 

77 X 29.6 X 300 

" — " = 20.7, 

33,000 " 

and the steam accounted for by the indicator per horse- 
power per hour is 593.34 -f- 20 .7 = 28.6 pounds. The 
steam actually used was of course considerably in ex- 
cess of this. 

It is not essential that the points x and y be taken 
at a distance equal to the clearance-line from the ends 
of the diagram, or that they be at equal distance from 
each end : the process consists in finding the volume, 
including clearance, at some point previous to exhaust- 
opening, and from the volume and pressure calculating 
the weight of steam, for convenience by the hour, and 
similarly finding the weight saved from some point in 
the compression-curve. Subtracting the latter quan- 
tity from the former gives the weight actually ex- 
hausted. When the points x and y can be conveni- 
ently located as represented, as they generally can be, 
it shortens the operation. 

It has been previously intimated that it was not al- 
ways an easy matter to determine by the diagram how 



MEASURING THE STEAM EXHAUSTED. 69 

much of the variation between the actual and the theo- 
retical curve was due to condensation and re-evaporation, 
and how much to leakages by valves and piston. In 
Fig. 14 it will be noticed that the actual curve falls be- 
low the theoretical soon after the steam -valve has 
closed. This is generally the case in an unjacketed 
cylinder, and is rationally enough accounted for by 
condensation in the cylinder, the difference in tempera- 
ture between the walls of the cylinder and the steam 
being greater than later in the stroke, and hence the 
conditions favorable for rapid condensation. But if 
the piston or exhaust - valve leak, the leakage will be 
greatest at this time, awing to the higher pressure of 
steam, and this may be taken to account for the fall in 
pressure. The real curve soon rises and crosses the 
theoretical curve, which may be accounted for by the 
re-evaporation of water by the excess of heat after 
the fall in pressure. But this increase of steam may 
also be accounted for by leakage of the steam-valve, 
which would naturally increase in amount as the pres- 
sure fell, while if the piston and exhaust-valve, either 
or both, leaked, the leakage by them would be corre- 
spondingly diminished. 

It will be noticed that the pressure rises very rapidly 
towards the end of the stroke, so much so as to point 
to the probability of a leaky steam-valve, which, it may 
be as well to state, was found to be the case. 

It may readily be seen that the leakage of valves and 
piston may be such as to assist in producing a more 
nearly correct expansion-curve than would result if 
they were tight, for which reason hasty conclusions as 
to the economy of an engine should not be drawn from 



7o 



INDICATOR PRACTICE. 



the quality of this curve, nor from the steam accounted 
for by the indicator. 

COMPUTING THE STEAM EXPENDED BY MEANS OF THOMP- 
SON^ TABLE. 

The following table, prepared by E. W. Thompson 
for the American Machinist, is in accordance with the 
plan for computing steam-consumption in use by the 




Fig. 15 — Scale 40. 

Buckeye Engine Company. The plan is illustrated in 
Fig. 15. To use the table the mean effective pressure 
must be known, but the horse-power, or the dimensions 
of the cylinder even, need not be known. Draw a ver- 
tical line at each end of the diagram exactly defining 
its length, and continue the expansion-curve guided by 
the eye to /, as if the exhaust had not opened. From / 



MEASURING THE STEAM EXHAUSTED. /I 

draw the line tC parallel with the atmospheric line. 
Measure the terminal pressure at / (from vacuum ), and 
find in the table, page 72, the number corresponding 
to it. In the table the numbers under T. P. represent 
the terminal pressure in pounds, and the figures at the 
head, 1, 2, 3, etc., tenths of a pound. If the terminal 
pressure is, say, 16 pounds, in the column against 16 
and under o. is 567.360, the required number. If the 
terminal pressure is, say, 20.6 pounds, against 20 and 
under 6 is 719.558, the number. 

Divide the number thus found by the mean effective 
pressure : the quotient will be the steam accounted for 
by the indicator per horse-power per hour, uncorrected 
for clearance and compression. To make this correc- 
tion multiply by the length of the line tE, and divide 
by the length of the line tC. 

It will sometimes happen that the maximum com- 
pression will not be as high as the terminal pressure. 
In that case tE will be longer than tC. When this 
occurs the compression-curve must be extended by the 
aid of the eye, as indicated at e, and E will be outside 
the diagram. When the maximum compression is 
higher than the terminal pressure tE will be shorter 
than tC. 

In Fig. 14 the terminal pressure is 28.3 pounds, and 
the mean effective pressure 44.6. In the table under 
3 and against 28 is 969.813, which divided by 44.6 = 
21.74. This is the steam-consumption uncorrected for 
clearance and compression. The length of tE is 3.2 
inches, and of tC 3.7 inches; 21.74 multiplied by 3.2 
and divided by 3.7 = 18.8, the pounds of dry steam 
exhausted per horse-power per hour. 



7 2 



INDICATOR PRACTICE. 



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MEASURING THE STEAM EXHAUSTED. 



73 



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74 INDICATOR PRACTICE, 

CHAPTER XL 
CONDENSING ENGINES. 

DIAGRAMS FROM A STEAM-JACKETED CYLINDER. 

So far as computing the horse-power is concerned, it 
is immaterial whether the diagram is from a condensing 
or from a non-condensing engine, the determination 
of the distance apart of the upper and lower lines be- 
ing all that is required in either case. But in a con- 
densing engine it is of interest to measure separately 
the work done above and below the atmosphere, so as 
to determine how much of all the work done to credit 
the condenser with. The pair of diagrams represented 
in Fig. 16 will serve to illustrate this, besides being in- 
teresting in other respects. They are from both ends 
of a cylinder 27" X 36", at a piston-speed of 90 feet per 
minute ; cylinder completely steam-jacketed, including 
the ends. The clearance is .026 of the piston-displace- 
ment. The approximate theoretical curve is drawn 
on one diagram from a point near release, and on the 
other from a point just after cut-off. The mean 
effective pressure of the right-hand diagram is 44.94, 
and of the left-hand 42.06 pounds, an average of 43.5 
pounds. The diameter of the piston-rod is 3.5 inches, and 
the mean net area of the piston 567.75 inches, so the 
horse-power for each pound mean effective pressure is 

567.75 X 1 _X9Q =I . S48 . 

33,000 



CONDENSING ENGINES, 



IS 




<S1 

I 






7& INDICATOR PRACTICE. 

The pressure exerted below the atmosphere is by the 
right-hand diagram 10.76, and by the left 11.82 pounds, 
an average of 11.29 pounds, — -nearly 26 per cent of the 
total mean effective pressure exerted. The indicated 
horse-power is 63.33, an< ^ the water per horse-power 
per hour accounted for by the indicator is 186 pounds. 
Of the prominent features of these diagrams the ad- 
mission-lines are good, as well as the steam-lines and 
cut-off, all of which is, of course, easy to bring about 
at the slow piston-speed. The expansion-curves show 
a remarkable departure from the theoretical curves, 
which is not easily accounted for if the steam-jackets 
prevent initial condensation. If, however, there was a 
good deal of initial condensation, the heat from the 
jackets may have re-evaporated the most of the water, 
and the increase of terminal pressure may have been 
due to this ; or it may have been due in part to the 
evaporation of water that entered the cylinder as 
water, and in part to leakage of steam-valves. What- 
ever it is due to, it represents a loss that may in part 
be seen by considering that the space a on the right- 
hand diagram represents work that might under better 
conditions have been done by the steam that was 
present in the cylinder at the opening of the exhaust- 
valves. Measuring this space, it amounts to an addi- 
tion of seven pounds to the mean effective pressure ; 
15.5 per cent more work might have been done by the 
steam exhausted. The terminal pressure is about 40 
per cent higher than it ought to be. It is not at all 
probable that such an amount of water entered with 
the steam, so that the most of the rise in pressure 
must be attributed to initial condensation and evapo- 






CONDENSING ENGINES. 77 

ration later in the stroke, and to leakage of steam- 
valves. 

In calculating the efficiency of a condensing engine, 
so far as the work done below the atmosphere is con- 
cerned, it is essential to know the vacuum in the con- 
denser; for, as in a non-condensing engine, the back- 
pressure that should be accounted against the cylinder 
is the difference between the line of counter-pressure 
and the atmospheric line, so in a condensing engine it 
is the difference between the line of counter-pressure 
and an imaginary line representing the pressure main- 
tained in the condenser. Calculated in this way, under 
the same conditions otherwise, the back-pressure in a 
condensing engine will be somewhat greater than in a 
non-condensing engine. In this instance the vacuum 
by gauge was 25 inches, in pounds 12.27. As the 
average pressure below atmosphere is 11.29, a small 
fraction of a pound being lost by compression, the re- 
sult in this respect is very good indeed. This small 
amount of back-pressure would have been reduced by 
about J pound if the exhaust-opening on the end repre- 
sented by the left-hand diagram had been a little earlier 
and more ample. Of course, at higher speeds the back- 
pressure would, with the same valves and valve-mo- 
tion, have been increased ; in fact, at high piston-speed 
it is not practicable to make the exhaust-openings so 
ample as to result in so little back-pressure as shown 
here. Altogether, these diagrams are excellent ones 
below the atmospheric line ; good ones above, so far 
as admission-lines, steam-lines, and release are con- 
cerned ; but decidedly poor ones so far as the expan- 
sion-curve has to do with their quality 



78 INDICATOR PRACTICE. 



DIAGRAMS FROM AN ENGINE CONDENSING AND NON-CON- 
DENSING COMPARED. 

The diagrams Fig. 17 represent graphically the 
effect of adding a condenser to a non-condensing en- 
gine. Both diagrams were taken on the same paper, 
as engraved — one with the condenser in use, and the 
other with the exhaust turned into the atmosphere. 
The fact that they were so taken, and that the load re- 
mained constant, makes it easy to compare them, and 
also makes the comparison more satisfactory. The 
engine from which they were taken is i8"X36", and at 
the time of taking the diagrams the revolutions were 
109, boiler-pressure 62 pounds, vacuum (by gauge) 24", 
40 spring. The clearance is four per cent of the pis- 
ton-displacement. 

The mean effective pressure of the two diagrams is 
the same — 28.32 pounds. The non-condensing diagram 
shows the terminal pressure to have been 24 pounds, 
the load — 142 horse-power — being too much for good 
economy calculated from the diagram ; or, to state it 
another way, and more correctly, the steam-pressure 
was too low for the load. The dry steam accounted 
for by the indicator was 25 pounds per horse-power per 
hour. The result with 20 pounds higher boiler-pressure 
would have been quite different. 

Comparing this with the condensing diagram, the ter- 
minal pressure by the latter is 14.5 pounds and the dry- 
steam exhausted 16.7 pounds per horse-power per hour: 
a remarkably good result for this steam-pressure and 
poor vacuum, for which, of course, the engine was not 
responsible. Looking at the general features of the 



CONDENSING ENGINES. 



79 



condensing diagram, the amount of compression is 
quite remarkable. This is brought about by the large 




CO 

I 



amount of inside lap. The inside lap — §" with f " out- 
side lap — probably accounts in part for a little more 



80 INDICATOR PRACTICE. 

back-pressure than might be expected, but from the 
fact that the exhaust-pipe is badly arranged, it is not 
certain how much of this back-pressure is due to the 
lack of exhaust-lead, and how much to the arrange- 
ment of the pipe. (The line nearest the vacuum-line 
V represents the pressure in the condenser, and is the 
one from which the back-pressure should be measured.) 
The faulty arrangement of the exhaust-pipe referred 
to is in running it down direct from the cylinder (the 
pipe is 6" diameter) for a short distance and then le- 
turning at an acute angle direct from the pipe leading 
down, without any enlargement or easing off of the 
bend whatever. Assuming that this bend in the ex- 
haust-pipe is the principal cause of back-pressure, it is 
still probable that an earlier opening of the exhaust- 
valve would reduce it slightly, since it would afford 
more time for the steam to pass the stricture in the 
pipe. Reducing the inside lap would correspondingly 
reduce the compression, but would probably leave 
sufficient to satisfactorily cushion the piston. The ex- 
haust-lap might probably be reduced to \ n or §", and 
then a little more steam-lead given to help up the 
compression, with satisfactory results, the slightly- 
rounded corner at b indicating that a little more steam- 
lead would do no harm otherwise. If this should re- 
sult in a pound less average back-pressure, it would 
make a decidedly good diagram still a little better. It 
is needless to say that the first thing that ought to be 
done is to rearrange the exhaust-pipe so as to get rid 
of the sharp bend. 

Points in the theoretical curve of the condensing 
diagram are indicated, beginning on the actual curve 



CONDENSING ENGINES. 8 1 

at the vertical line e. It will be seen that the theoret- 
ical and actual curves agree exactly at each end, but 
that the latter falls a little below the former at the 
middle. This is what should be with ordinary dry 
steam, unjacketed cylinder and tight valves. The cut- 
off is reasonably sharp for the piston-speed, and the 
steam line good. Larger ports would give a little 
straighter steam-line, but there is the question if the 
loss otherwise would not more than balance any gain 
that would result. 

The distance of the atmospheric line A, below the 
point of terminal pressure of the non-condensing dia- 
gram, is almost exactly equal to the distance of the 
line of condenser-pressure below the terminal pressure 
of the condensing diagrams ; hence, if the steam es- 
cape with equal facility in both instances, the back- 
pressure of the two diagrams should be equal. But 
the back-pressure, as usual, is the greatest in the con- 
densing diagram, which would be an argument in the 
direction of what is generally believed, viz., that the 
exhaust-passages for a condensing engine should be 
larger than for the same engine worked non-condens- 
ing. If the pressure in the condenser was quite steady 
at that noted, it is reasonably certain that the steam 
did not, under the same conditions, escape as readily 
into the condenser as into the atmosphere. But the 
regular decline of the line of counter-pressure of the 
condensing diagram, quite up to the point of exhaust- 
closure, points to the probability that the condenser — 
perhaps from being too small — did not " get hold" 
quite promptly, and that the pressure in it fluctuated 
considerably. 
6 



82 INDICATOR PRACTICE. 

The condensing diagram shows that 25 per cent of 
the work is done below the atmosphere, and it is 
customary in such cases to credit the condenser with 
this amount. This is neither theoretically nor practi- 
cally correct, because it assumes that if the engine was 
run non-condensing there would be no back-pressure, 
which is not so, and which, in such a calculation, 
would, so far as it goes, not give the condenser suffi- 
cient credit. It is also assumed that condensation in 
the cylinder would be the same whether the engine 
was run condensing or non-condensing, which also is 
not true, and which would tend to credit the conden- 
ser with more than its due. The compression is also 
different in the two instances, which further compli- 
cates the comparison. The only intelligible compari- 
son that can be made is with the load in one instance 
equal to that in the other, as the pertinent question is 
how much the condenser will save in doing a definite 
amount of work. The steam accounted for by the in- 
dicator being in one instance 25 and in the other 16.7 
pounds per horse-power per hour, the percentage in 
favor of the condenser is 33. The percentage of gain 
will not be so much as this, because of greater loss 
from condensation when the engine is condensing; it 
also costs something to operate the air-pump. It 
would not be safe to estimate the saving due to the 
use of the condenser at more than 25 per cent ; but 
this conclusion is not reached because 25 per cent of 
the work happens to be done below the atmosphere. 
If the engine was to run non-condensing with this 
load, higher steam-pressure should be carried, which 
would increase the economy, making the difference 



CONDENSING ENGINES. 83 

still less. The economy of the engine running con- 
densing would be better, theoretically, with steam of 
higher pressure, but perhaps not actually better. 

Mention was made of the rounded corner in the 
admission-line. This is not especially, if in any de- 
gree, objectionable. It was only alluded to as show- 
ing that a little more lead might, for another purpose, 
be given. With the engine working non-condensing 
the cylinder is warmer and the rounded corner does 
not appear, indicating what is generally found to be 
true, viz., that a condensing engine requires more 
lead than one worked non-condensing. 

COMPOUND CONDENSING-ENGINE DIAGRAMS. 

The diagrams Figs. 18, 19, and 20 are from a pair 
of 18" X A 2 " automatic cut-off engines, compounded by 
adding an independent engine, with cylinder 40" di- 
ameter, 42^" stroke of piston. The high-pressure en- 
gines run at a speed of 83 and the low-pressure engine 
at 88 revolutions per minute. Figs. 18 and 19 are 
from the high-pressure cylinders, and Fig. 20 from the 
low-pressure cylinder. 

The high-pressure diagrams show an initial pressure 
nearly equal to boiler-pressure (65 pounds), which 
owing to the piston-speed, falls off considerably before 
the point of cut-off is reached. In fact, the points of 
cut-off cannot be located with any degree of accuracy. 
The lead is unequal, and rather excessive, although it 
brings about a little higher initial pressure than would 
otherwise result, and probably does no particular harm 
if it results in smooth running. The points of exhaust 
opening and closure, also, are not alike. The time of 



8 4 



INDICATOR PRACTICE. 




CONDENSING ENGINES. 



85 




w 






86 INDICATOR PRACTICE. 

exhaust-opening can be seen on the diagrams in Fig. 
18, being indicated by a change from the direction of 
the expansion-lines, the pressure in the cylinder rising, 
instead of falling, as is usually the case when the ex- 
haust-valve opens. This is due to the pressure in the 
steam-chest of the low-pressure cylinder being higher, 
at just this time, than the pressure of the expanded 
steam in the cylinder. The variation in pressure of 
the steam in the low-pressure steam-chest accounts for 
the unevenness of the lines of counter-pressure on the 
high-pressure diagrams. These diagrams, especially 
those in Fig. 19, show that the cut-off is not very well 
equalized. If steam had been worked alike in both 
ends of the cylinder, the expansion-curves would have 
crossed each other midway of the lengths of the dia- 
grams — an end more nearly attained in Fig. 18 than in 
Fig. 19. 

The diagrams from the low-pressure cylinder show 
very straight steam-lines, and a little inequality as to 
the amount of work done in the two ends of the cylin- 
der, in the lead, and in the amount of the back-pres- 
sure. Of course, if thought desirable, the lead could 
be readily equalized as well as the cut-off, which is 
equally true of the high-pressure cylinders. The dif- 
ference in back-pressure, between the two diagrams 
(Fig. 20), is more apparent on account of the low ten- 
sion of the spring used in the indicator. It really 
amounts to less than \ pound. 

In respect to hastily observing diagrams, it should 
be noted that in those taken with a spring of low ten- 
sion, variations in the lines appear magnified to the 
eye, since diagrams are commonly taken with springs 



CONDENSING ENGINES. 



87 




1 



88 INDICATOR PRACTICE. 

of comparatively high tension, and the eye becomes 
educated to read them on this basis. In the instance 
of these diagrams a variation of one pound pressure 
is represented by -^ of an inch, which is a very notice- 
able quantity. 

The mean effective pressure (average of both cylin- 
ders) of the high-pressure diagrams is 23.8 pounds, and 
the horse-power 212.8. The mean effective pressure 
of the low-pressure diagrams is 8.62 pounds; horse-pow- 
er, 204.5 I total horse-power developed, 417.3. It is in- 
teresting to determine just how much the work done is 
increased by the addition of the low-pressure engine. 
If it is assumed that the average back-pressure of the 
high-pressure cylinders exhausting the quantity of 
steam used into the atmosphere would be one pound, 
the loss of mean effective pressure in these cylinders 
due to exhausting into the steam-chest of the low- 
pressure cylinder is 7 pounds, equivalent to 62.5 horse- 
power, the remainder — 142 horse-power — being the 
work done by the low-pressure engine, without any 
cost in steam. This is not giving the low-pressure en- 
gine all the credit due it, because the higher pressure 
of steam in the high-pressure cylinders during the 
period of exhaust keeps them hotter, and reduces the 
inevitable loss from condensation. 

It has been previously remarked that it is essential 
to know the pressure in the condenser, in order to 
determine how much back-pressure to charge against 
the cylinder. This is particularly important in this 
instance, since the condenser and air-pump were no 
part of the low-pressure engine, but were quite inde- 
pendent, located more than 50 feet away (measured 



CONDENSING ENGINES. 89 

by the length of connecting-pipe), and some distance 
higher than the cylinder. The exhaust from the 
engine passes from the cylinder down to a heater 
30 inches diameter and 16^ feet long, then up and 
to the condenser. The vacuum-guage on the con- 
denser showed a vacuum of 23 inches, or a pressure 
of 3.4 pounds, as represented by the line on the 
diagrams. Measuring from this, the back-pressure 
which the engine is responsible for is only 2 pounds. 
The heat extracted from the exhaust-steam in the 
heater referred to was used for heating water to be 
employed for various purposes in the mill, and it is to 
be presumed that the loss from impaired vacuum was 
more than made good by the heat saved in this way. 



90 IND1CA TOR PRA CT1CB. 



CHAPTER XII. 

DIAGRAMS REPRESENTING VARIOUS 
PEC ULIARITIES. 

IMPROPER ACTION OF CUT-OFF VALVE, AND RESTRICTED 

EXHAUST. 

THE application of the indicator to the cylinder of 
a steam-engine not infrequently reveals curious con- 
ditions, and affords instructive texts against dispensing 
with the use of that instrument. The diagram in Fig. 
21 was taken from a cylinder i8^ // X48 // , the engine 
running at 35 revolutions per minute; and the most 
interesting feature of the case is that it had been 
running ten years, all the time in condition to make 
just such a diagram. The cylinder had never been 
drilled for the indicator until the time when this dia- 
gram was taken, and then the indicator was applied to 
determine the horse-power used, the intention being to 
put in a new engine, not because this one did not work 
satisfactorily, but because it was believed to be over- 
loaded, the estimate being that it was loaded to be- 
tween 100 and 200 horse -power. The engine had 
originally a plain slide-valve, but had been changed to 
an automatic cut-off, the steam being cut off by a valve 
outside the steam-chest, the time of closing of which 
was under control of the governor. This kind of 
valve-motion is usually operated from the main valve 



VARIOUS DIAGRAMS. 



91 



rock-arm or eccentric rod, the motion being the same 
in direction as that of the main valve; but the lap 







being nothing, or less than that of the main slide, pro- 
vides for its opening in advance of the latter. In this 



92 INDICATOR PRACTICE. 

instance, however, it was operated by a separate eccen 
trie, which was undoubtedly unfortunate, as if motion 
had been communicated by the main rock -arm, it 
would hardly have been possible to have arranged it so 
badly. 

The boiler-pressure was 6oJ pounds, out of which an 
initial pressure of 30 pounds was realized, with a steam- 
line that struggled along up to 42 pounds at half-stroke, 
when the cut-off occurred. The point of cut-off is well 
defined, showing a sharp closure of the cut-off valve. 
This, with the compression and admission lines, are the 
only tolerable features of the diagram. From the 
point of cut-off the pressure falls only 18 pounds by 
expansion, the volume of steam in the steam -chest 
operating as clearance so far as expansion is concerned. 
What this clearance amounts to, illustrated by length 
added to the diagram, can be approximately deter- 
mined. 

Taking a point at a, directly after cut-off, the pres- 
sure from vacuum is 52 pounds, and at the end of the 
stroke it is 39 pounds ; that is, the pressure at the end 
of the stroke is ff = f what it is at a. As the pres- 
sure varies inversely as the volume, the volume repre- 
sented from a to the end of the stroke is one quarter 
of the total volume represented from the clearance-line 
to the end of stroke. The distance from a to the end 
of the diagram is if inches ; hence the whole volume 
would be represented by a length of if X 4 = 7 inches, 
that is, the clearance-line must be drawn 7 inches from 
the end of the diagram, or about 2f inches from the 
beginning. This enormous clearance (in the steam- 
chest) has only to do with expansion, because before 



VARIOUS DIAGRAMS. 93 

the exhaust opens the communication between the 
steam-chest and cylinder is closed by the main valve. 
But it neutralizes the gain that would otherwise result 
from expansion. 

The horse-power developed is 60, and the dry steam 
exhausted is 48^ pounds per horse-power per hour — at 
least twice what it ought to be. How much water 
was exhausted is not known, but there was so much in 
the cylinder that it was scarcely safe to keep the cylin- 
der-cocks closed while taking a diagram. Alternate 
heating and cooling the large metallic surfaces inside 
the steam-chest doubtless contributed to increase the 
amount of water present in the cylinder ; this is always 
good argument against any cut-off arrangement in the 
use of which large surfaces of metal (other than those 
absolutely necessary) are subjected to alternate heat- 
ing and cooling at every stroke. 

Probably not less than 7 pounds of coal per horse- 
power per hour were used — say a ton a day more than 
should have been required. The engine had been run- 
ning ten years in this condition, in which time it had 
wasted coal worth $15,000. 

The cause of this is plainly shown by the diagram. 
Beginning with the compression -line, the pressure 
comes up very satisfactorily to 30 pounds, when the 
main valve opens the steam-port ; but instead of the 
pressure rising to within a pound or two of boiler-pres- 
sure, as the piston advances it falls to 26 pounds at 
about one eighth of the stroke. The reason of this is 
that the cut-off valve is behind, and has not opened 
for the admission of steam to the steam-chest, so that 
the only steam available for use in the cylinder for 



94 INDICATOR PRACTICE. 

more than 6 inches of the stroke is that left in the 
steam-chest at the end of expansion in the other end 
of the cylinder and what leaked in past the poorly fit- 
ting cut-off valve. At about one eighth of the stroke, 
the cut-off valve, which should have opened early 
enough to have provided steam at full boiler-pressure 
in the steam-chest before the main valve uncovered 
the steam-port, begins to open slowly, and the pres- 
sure in the cylinder crawls up, so that the cut-off that 
should have taken place at less than one-quarter stroke 
takes place at one-half stroke. Then the volume of 
steam in the steam-chest, together with that in the 
cylinder, is expanded to about 40 pounds, absolute, 
instead of to 20 pounds, or less, as it would have been 
under favorable conditions. The exhaust opens late 
and the counter-pressure falls slowly, the back pressure 
being 5 pounds, when, at that speed, it should not 
have been more than one-half pound — a clear loss of 
more than 10 horse-power. 

Altogether, it would be difficult to find worse con- 
ditions in an automatic engine, and it is safe to say 
that the application of the indicator ten years earlier 
would have pointed out a way to a very satisfactory 
saving. Such changes, for instance, as a steam-chest 
with the least practicable amount of unoccupied room, 
to reduce the clearance during expansion ; a main 
valve with more steam lap and more travel, so that 
the exhaust would have opened earlier and more 
rapidly, thus reducing the back pressure, and the cut- 
off eccentric advanced so as to open the cut-off valve 
in advance of the main valve, would have been sug- 
gested by the first diagram taken. It is believed that 



VARIOUS DIAGRAMS. 95 

the cut-off valve was adjusted for the late opening to 
make it possible to obtain a later cut-off than other- 
wise, under the impression that the capacity of the 
engine would be increased by this means. If so, the 
attempt was a first-class failure, as materially more 
work could have been done by setting the cut-off ec- 
centric so as to get steam of very near boiler-pressure 
in the cylinder, and cutting off correspondingly early 
in the stroke. 

PECULIARITIES OF EXPANSION-LINES — REOPENING OF 
STEAM-VALVE. 

Diagram 22 shows peculiarities in the expansion- 
line which are sometimes taken as representing im- 
proper action of the indicator. The real cause is worth 
investigation. It will be noticed that the expansion-line 
from a to b is substantially vertical in direction. This 
is only observed where the clearance is small. In such 
instances the pressure in the cylinder falls very rapidly 
directly after cut-off, because a small movement of the 
piston will serve to increase largely the volume of steam 
in the cylinder as compared with the volume at cut-off, 
and correspondingly decrease the pressure. In the 
cylinder from which this diagram was taken the clear- 
ance marked on the diagram is .0253 of the displace- 
ment of the piston, and the cut-off is about y 1 ^ of the 
stroke. The steam being cut off with the suddenness 
of a blow at a, the piston travelling at a mean speed of 
between 500 and 600 feet per minute, and the distance 
horizontally from a to b representing less than one-inch 
motion of the piston, it will be seen that the pressure 
under the indicator-piston is almost instantly very ma- 



9 6 



INDICATOR PRACTICE. 



terially reduced. The spring being under considerable 
tension starts the indicator-piston down, and the mo- 




I 

6 



mentum which it soon acquires carries the pencil ahead 
of the position due to the steam-pressure, precisely as 
in diagrams from high-speed engines, or in those taken 



VARIOUS DIAGRAMS. 97 

with a light spring, the pencil is found alternately too 
low and too high, the result being, a little later in the 
stroke, a regularly undulating line that is correctly taken 
as evidence of correct action of the indicator. In these 
instances the pencil will fall below its correct position, 
then the reaction will carry it above, and so on. In 
this instance the first evidence of reaction is at b, which 
is where the reciprocating parts of the indicator recover 
from the effects of their downward impetus. Had this 
occurred later the pencil would have been carried up 
considerably out of its true course, but at this early 
point in the stroke the pressure is falling too rapidly 
for this to occur, so that the reaction amounts to 
scarcely more than a pause in the downward motion. 
Below b a short distance there is another pause, after 
which the expansion-line gets into proper shape, being 
assisted by the more gradual fall in pressure as the 
volume of steam is increased. As previously noted, 
had precisely the same thing occurred later in the 
stroke, as from a cut-off when the volume of steam in 
the cylinder was twice or three times as great, the re- 
sult would have been the wavy expansion-line fre- 
quently seen. 

But there is still another cause that tends to pro- 
duce a straight line from a to b. As has been pre- 
viously explained, the actual curve of the diagram is 
usually found below the theoretical curve directly 
after cut-off, especially where full steam is worked for 
a small fraction of the stroke only, from the fact that 
condensation is taking place with great rapidity to 
supply the heat lost by the exposed surfaces during 
expansion and exhaust ; so that taking into considera- 
7 



9 8 



INDICATOR PRACTICE. 



tion both these causes, each operating in the same 
direction, the position of the line from a to b is logi- 
cally accounted for without attributing any fault to 







the indicator, which, so far as can be seen from the dia- 
gram, was in good working condition. Finally, draw- 
ing the theoretical curve from the point of cut-off, the 






Various diagrams. 99 

variation is not nearly so great as a glance at the dia- 
gram would seem to indicate. A part of this curve is 
drawn in dotted line, and shows the variation a little 
greater than it actually is. 

Diagram 23 shows peculiarities that cannot be ex- 
plained in this way. The initial pressure was 60 
pounds — one pound less than boiler-pressure — and the 
valve closed very sharply at c, after the piston had 
made a small fraction — about 5 per cent — of its stroke. 
The effort to recover after the usual somewhat too 
rapid fall of the pencil is seen at d y and from some 
cause the pressure rises again to nearly 60 pounds, 
making, apparently, two points, c, c ', of cut-off. The 
cause of this was that the cut-off valve, which dropped 
in closing, afterward left its seat, and from the ampli- 
tude of the steam -ports actually admitted steam of 
nearly boiler-pressure the second time. From a short 
distance below c f the line falls too slowly for some dis- 
tance, showing that the valve leaked while settling 
back against its seat. The engine from which this 
diagram was taken was a small one, and the aggregate 
length of the ports controlled by the cut-off valve was 
equal to about twice the diameter of the cylinder. 
With this length of port the cut-off proper occurred 
while the valve was dropping at its highest velocity, 
and through only a very short distance. The effect of 
this was that the pressure in the cylinder was not re- 
duced enough while the valve was closing so that the 
unbalanced pressure in the steam-chest would hold the 
valve to its seat against the jar of the air-cushion which 
stopped it. 

There were two remedies that suggested them- 



100 



INDICATOR PRACTICE. 



selves, one of which was to provide for closing the 
valve slower, and the other to arrange a guard to pre- 




vent the valve leaving the seat, horizontally, 
remedy was the one tried, with success. 



The last 






VARIOUS DIAGRAMS. IOI 

Trouble similar to this, though not so marked in 
extent, often occurs in four-valve engines. The result 
generally appears somewhat later in the stroke in the 
form of an irregularity in the expansion-line, as at a, 
Fig. 24, followed by an expansion-line much too high, 
and high terminal pressure. This is usually explained 
as being the result of wet steam, a small cylinder, or in 
any but the correct way. The true explanation is that 
the valve does not close properly, or reopens a little, 
and does not get properly seated until some distance 
beyond where cut-off apparently takes place. It is 
needless saying that this diagram represents an im- 
portant waste of steam. 

ECCENTRIC OUT OF PLACE. 

Diagram 25 was referred to the writer for explana- 
tion on the supposition that the admission-line was at 
the left, and that cut-off was at e, the query being, Why 
the expansion -line got down so low at b? It was 
known that the eccentric was out of position when the 
diagram was taken. A little reflection showed that it 
was a mistake to suppose the left to be the admission 
end of the diagram, and starting wrong efforts to read 
it were of course fruitless. Why this conclusion was 
arrived at is the special feature of interest, as it will 
generally aid in unravelling " crooked " diagrams. The 
reasoning was as follows : If the admission was at the 
left, then dc is the admission-line and cb the expansion- 
curve. But dc is an impossible admission-line (for late 
admission) because it curves downwards, and cd is an 
impossible expansion-line because it curves upwards. 

It would, perhaps, be possible by bringing about 



102 



INDICATOR PRACTICE. 



peculiar leaks to get either of these lines, but it is en- 
tirely improbable that leaks occurring in the ordinary 
way should be responsible for changing the direction 




of flexure of either as shown. When it comes to so 
changing both lines, the possibility of it is not worth 
consideration. 



VARIOUS DIAGRAMS. IO3 

Beginning at the other end of the diagram, — at the 
right, — the reading of it is plain enough : At a the 
piston begins to move ahead, but the valve being be- 
hind time the admission-port is covered. There is at 
this time a pressure of 26 pounds absolute in the 
clearance-space. The piston moving along and the 
port remaining covered, the pressure falls by expan- 
sion to b. At this point — about one-quarter stroke — 
the valve begins to open the port, but the motion of 
the piston is so rapid and the space to be filled with 
steam so large that the pressure increases slowly, as 
represented by the line be; it is in respect to this line 
an aggravated case of late admission without assist- 
ance from compression. Under these conditions the 
upward flexure of the line be is accounted for; it is 
exactly what would be expected. 

At c steam is cut off ; cd is the expansion-line, con- 
cave downward and inward as it should be. The ex- 
haust opens late at d, for which reason the pressure 
falls slowly, till beyond e it is equal to that against 
which the piston is working. The line from d, by ^, 
to a is the line of counter-pressure, there being no 
compression. 

The engine from which this diagram was taken is 
22" X 30", running at 75 revolutions. The engine 
kept running, doing its regular work with the mis- 
placed eccentric, but pounded so badly the indicator 
was applied to ascertain the cause. The exhaust was 
against the high pressure shown, because the exhaust- 
steam at that pressure was used for other purposes 
requiring that pressure. But for this use of the ex- 
haust-steam the trouble would have manifested itself 
at the coal-pile. 



104 INDICATOR PRACTICE. 



CHAPTER XIII. 
INITIAL EXPANSION— SMALL STLAM-PIPE. 

ECONOMY OF INITIAL EXPANSION. 

The greatest economy in the use of steam in the 
steam-engine being, broadly speaking, when the ter- 
minal pressure is lowest compared with the mean 
effective pressure, it follows that a fall of pressure in 
the cylinder previous to cut-off, usually called initial 
expansion, represents a loss when occurring in an 
automatic cut-off engine, because it makes the cut-off 
occur later than it otherwise would, increasing to a 
corresponding extent the terminal pressure. Hence, 
in this type of engine the effort is made to provide for 
a steam-line as straight and as near boiler-pressure as 
practicable without sacrificing too much in some other 
direction to obtain it. There is undoubtedly a point 
in all ordinarily constructed engines beyond which it 
is the reverse of economical to go in this direction — a 
point somewhere short of boiler-pressure in the cylin- 
der, and short of an absolutely straight steam-line. 
Just how far it represents economy in the use of 
steam to go in the direction of a perfect steam-line 
depends upon a variety of circumstances. Small 
valves do not consume so much of the power of the 
engine in their operation as larger ones (of the same 
kind), and as there is inevitably some leakage, it is 



INITIAL EXPANSION— SMALL STEAM-PIPE. 105 

naturally greater where the ports are long than where 
they are short ; it is also understood that a balanced 
valve moves easier than an unbalanced one — all of 
which is entitled to consideration in determining what 
the character of the steam-line should be. 

But while it is true that initial expansion, to any 
great extent, usually represents a loss of economy in 




Fig. 26 — Scale 30. 



the instance of an engine in which the governor oper- 
ates to vary the point of cut-off, it is equally true that 
when the cut-off is fixed and the speed controlled by 
means of a throttling governor, initial expansion usu- 
ally represents gain, sometimes in a marked degree. 
This is because it then has the effect of bringing about 
lower terminal pressure for a given mean effective 
pressure. 

While initial expansion is, perhaps, properly enough 



106 INDICATOR PRACTICE. 

called throttling, the distinction should be sharply 
made between throttling that results only in reducing 
the initial pressure, and that which provides for a 
gradual fall in the pressure from that nearly equal to 
boiler-pressure to a point materially lower at cut-off. 

The diagram, Fig. 26 (in full lines), shows a fair 
amount of initial expansion, and will illustrate the 
gain brought about by it, which may be more or less, 
according to circumstances. It is from a 12" X 20" 
engine, running at 90 revolutions, valve adjusted to 
cut-off at 11", or at c on the diagram. The boiler- 
pressure was 50 pounds, 39 pounds of which was 
realized in the cylinder at the beginning of the stroke, 
the pressure falling from that pressure at b, to 22 
pounds at c, by initial expansion, and then by regular 
expansion to a terminal pressure, t, of 24 pounds ab- 
solute. The gain by initial expansion may be deter- 
mined by comparing the actual diagram with the one 
plotted in dotted lines, both diagrams representing 
equal work. In the latter the pressure remains con- 
stant from b' to c\ the initial pressure being 27 pounds, 
or that required with the straight steam-line to make 
the mean effective pressure equal that of the actual 
diagram. Since the mean effective pressures of the 
two diagrams are the same, we can approximate the 
saving from initial expansion by calculations from the 
weight of steam at pressures / and t ' . The pressure 
(absolute) at / is 24 pounds, and the weight per cubic 
foot at that pressure .0610 pound. At /' the pressure 
is 27 pounds, weight of a cubic foot .0683 pound ; dif- 
ference, .0073 pound, or about 11 per cent. If the 
saving from exhaust-closure were accounted for, this 



INITIAL EXPANSION— SMALL STEAM-PIPE. 10? 

percentage would be increased; but n per cent is a 
safe estimate in this case, letting the saving from ex- 
haust-closure offset a little more condensation as the 
result of admitting steam of higher pressure. 

The steam-lines of diagrams from engines in which 
the speed is controlled by throttling will be of a 
variety of forms, according to existing conditions and 
the construction of the engine. There is quite as 
much difference in the economy of such engines, 
whether fitted with separate expansion-valves or not, 
as there is between different automatic cut-off engines, 
and it is just as readily determined by the use of the 
indicator, notwithstanding which the indicator is sel- 
dom applied to this class of steam-engines. Its intelli- 
gent use, changing the construction in accordance with 
what was learned from its indications, would result in 
as much gain in efficiency, comparatively, as has been 
the case in the instance of the automatic cut-off en- 
gine. 

DIAGRAMS FROM THE SAME ENGINE WITH SMALL AND 
LARGE STEAM-PIPES. 

The effect of using a small steam pipe, for an auto- 
matic engine, by which initial pressure is reduced and 
expansion shortened, resulting in high terminal pres- 
sure, may be seen by a comparison of diagrams 27 
and 28. They were taken from an automatic engine 
12" X 30", at a speed of 95 revolutions per minute. 
When 27 was taken, steam was supplied through 30 
feet of 2-J-inch pipe, with three elbows in its length. 
Diagram 28 was taken after a four-inch pipe had been 
substituted. 



io8 



INDICATOR PRACTICE. 



Diagram 27 shows, as compared with 28, a loss 
equal to \2\ per cent in steam used, and it also shows 




that in an emergency but little more work could be 
got from the engine ; a small increase of work, or re- 
duction in steam-pressure, and the engine would not 



INITIAL EXPANSION— SMALL STEAM-PIPE. I(X) 

run up to speed. Even when running under the con- 
ditions shown, in changes of load, such as throwing 








on machinery that had been thrown off, it would be 
found that the governor had but little control over the 
motion ; in other words, that the engine would be 



IIO INDICATOR PRACTICE. 

very slow in getting up to speed. The loss in this 
respect might, in some kinds of work, be more serious 
than the loss of steam. 

With the large steam-pipe in use when 28 was taken 
there is a fair margin for governing, either when the 
steam-pressure is reduced, or the load increased, be- 
cause with the higher initial pressure the required 
mean effective pressure is had with a cut-off at one- 
quarter stroke, while if necessary steam may be ad- 
mitted till a little later than half-stroke. With the 
large steam-pipe the high mean effective and low 
terminal pressure necessary to economy is had. 

It is always best in any engine to have the steam- 
pipe of ample size ; then, if it is desirable to bring 
about a reduction of initial pressure, do it by throt- 
tling. 



DETECTING LEAKY VALVES. Ill 



CHAPTER XIV. 

DETECTING LEAKY VALVES— LIGHT FLY- 
WHEEL. 

LEAKY STEAM AND EXHAUST VALVES. 

Diagrams Fig. 29 are from a four-valve engine 20" X 
60", running at 57 revolutions; boiler-pressure about 
jo pounds. They are not good ones. The cut-off is not 
as prompt as it usually is in this class of engines, and 
the exhaust opens too late. This late exhaust-open- 
ing results in a material loss from back-pressure at and 
near the beginning of the return stroke in B, and sub- 
stantially the same loss would undoubtedly be shown 
in A if the terminal pressure were not so much lower. 

Another fault is that the work done is not equalized 
between the two ends. This equalization should be 
brought about, and the exhaust-valves opened at least 
two inches earlier in the stroke. 

But the diagrams show evidence of a graver fault 
than either of these, viz., leaky valves. While the 
indicator cannot always be relied upon to detect leaky 
valves and piston if the leak is small, when it is large 
it will do so in almost every instance if diagrams are 
taken from both ends of the cylinder. Leakage of 
steam into or out of the cylinder will influence the 
character of the expansion-curve. If steam leaks out 
of the cylinder the terminal pressure will be lower than 



112 



INDICATOR PRACTICE. 




I 



DETECTING LEAKY VALVES. 113 

it otherwise would be ; if it leaks into the cylinder it 
will be higher. If both steam and exhaust valves leak, 
the leaks might possibly balance each other, but there 
is no probability that this would be the case in each 
end of the cylinder. 

At a piston-speed of 400 to 600 feet per minute, the 
terminal pressure should not, in cylinders of 12 inches 
and upward in diameter, be more than 2 pounds above 
the termination of the theoretical curve. If found 
higher than this, there is a probability of leaky steam- 
valves. If the theoretical curve ends lower than the 
actual curve, the presumption is that t the exhaust-valves 
or the piston leaks. 

In Fig. 14, the theoretical curve, drawn from a point 
just after cut-off, showed a terminal pressure so high as 
to lead to the belief that steam leaked into the cylin- 
der. In the instance of Fig. 29, it is difficult to tell, 
even approximately, where cut-off occurred, so a dif- 
ferent plan is pursued ; that is, the curves are drawn 
from a point a just before exhaust-opening. They 
show just as clearly that in B there is a good deal 
more steam present at the termination of the stroke 
than at cut-off, wherever it may have been, and that in 
A there was about as much less. There is every rea- 
son to conclude that in one instance steam leaks freely 
into the cylinder, and that in the other it leaks out 
about as freely. All the valves, steam and exhaust, 
probably leak, but on one end the steam-valve leaks 
most, while the same is true of the exhaust-valve on 
the other end. If both diagrams were like A, the leak 
might all be by the piston. If both were like B, it 
would be possible, but highly improbable, at this pis- 
8 



114 INDICATOR PRACTICE. 

ton-speed that re-evaporation in the cylinder was the 
cause of the increased quantity of steam present. 
There would not be time at a piston-speed of nearly 
600 feet to condense sufficient water to increase the 
quantity of steam to such an extent, or time to re- 
evaporate it if it entered the cylinder as water. 

It may be remarked, that when a little too much 
steam is found in the cylinder at the end of the stroke, 
as indicated by the expansion curve drawn from near 
exhaust-opening keeping just sensibly above the real 
curve, or the curve drawn from near cut-off falling a 
pound or two below it near the end of the stroke, it is 
accounted for, usually, by re-evaporation in the cylin- 
der. But when too small an amount of steam is found 
it is evidence of leak; this refers to the use of ordi- 
nary steam, that is, steam that is not superheated. 

There is evidence enough in either of these diagrams, 
considered singly, to lead to a belief that the valves 
were leaky ; taken together, the evidence is conclu- 
sive. 

When we have a pair of diagrams like these it is 
generally possible to detect leaky valves without know- 
ing the clearance, which is necessary for drawing the 
correct theoretical curves. Thus in this instance the 
clearance might be assumed to be anything, say 6 per 
cent. Upon this assumption, if the theoretical curves 
were drawn they would still show that in one diagram 
there was too much steam at exhaust-opening, and in 
the other not so much as there should be. When 
leaks exist to the extent here indicated, there is a very 
serious loss of steam. 



DETECTING LEAKY VALVES. 



"5 



A LIGHT FLY-WHEEL. 

The diagrams in Fig. 30 illustrate an aggravated case 
of attempting to bring about good regulation in a 
throttling-engine provided with a fly-wheel too light 
for the purpose. The fly-wheel has an important bear- 
ing on the fuel economy of any engine, either throt- 




Fig. 30— Scale 40. 

tling or automatic cut-off, but unfortunately in the 
throttling-engine this receives but little consideration. 

The steam-line of this diagram (in full lines) has, at 
the beginning, the proper direction for producing a 
good throttling diagram — that is, good for the amount 
of work being done ; — but somewhat la^er than half- 
stroke, the governor-valve opens suddenly, apparently 
its full capacity, admitting steam till near the end of 
the stroke the pressure exceeds the initial pressure by 



Il6 INDICATOR PRACTICE. 

six pounds, and this at a time when the steam thus ad- 
mitted can do but little work before it is exhausted. 
This admission of steam late in the stroke, so that the 
terminal pressure measured from atmosphere is, in 
some instances, equal to or higher than the mean effec- 
tive pressure, is the loss likely to result from the at- 
tempt to use a light fly-wheel and a good governor. 
Years ago, when governors were in use that began to 
act some seconds after a variation in speed, the waste- 
ful effects of a light fly-wheel were not so noticeable, be- 
cause it was as good as the governor, which had not 
sufficient energy to waste much steam. But with the 
modern high-speeded regulator, that almost anticipates 
change of speed, good steam-economy cannot be ex- 
pected without proper dimensions of fly-wheel. 

The engine from which this diagram was taken was 
bought second-hand, but was in good condition and 
had well-designed, ample ports. It had, also, a fairly- 
proportioned fly-wheel pulley, but it being inconveni- 
ent to belt from this fly-wheel, and a fly-wheel being 
nothing more than a pulley to the parties who bought 
and put the engine up, a pulley of less diameter and 
less than one quarter the weight was substituted. 

Starting at the beginning of the stroke, and assum- 
ing the diagram from the other end of the cylinder to 
have been a duplicate of this (which it was very nearly), 
the action of the governor and influence of lack of fly- 
wheel can be studied. Thus the speed may be as- 
sumed to be normal at the beginning, and the governor- 
valve in about the right position, but the steam-chest 
pressure is too low. With the light wheel and the low 
steam-chest pressure, the speed falls off, so that at 



DETECTING LEAKY VALVES, II7 

about mid-stroke the governor is induced to act, which 
it does by fully opening the valve ; then, there being 
but little resistance in the wheel, the speed is acceler- 
ated sufficiently to quite close the governor-valve at 
about the time the lap of the slide-valve operates to 
cut off steam. It seems probable that the governor- 
valve remained closed until about the time steam was 
admitted for the return stroke, or a little later, the 
steam required to fill the clearance-space accounting 
for the initial pressure being less than the pressure in 
the steam-chest at the time of cut-off. To make this 
diagram would require about 75 pounds of water per 
horse-power per hour, and the boiler required such 
hard firing to evaporate the quantity of water nec- 
essary, that more than 12 pounds of coal per horse- 
power were burned ; in fact, but for the difficulty in 
keeping steam, the engine might still have been run- 
ning as it was when this diagram was taken, as the 
governor kept the speed in revolutions per minute very 
regular, and the indicator was applied to the engine 
because the boiler was too small. 

To remedy matters, and keep the small pulley to 
belt from, a fly-wheel with a narrow and deep rim was 
put on beside the pulley, and without further change 
the diagram shown in dotted lines was taken. This is 
a very good throttling diagram, with the exception 
that the cylinder is too large for the work, which 
brings about low initial pressure. The water required 
when this diagram was taken would be about 50 in 
place of 75 pounds — a saving of 33 per cent. The 
saving in coal was more than this, as decreased con- 
sumption brought about more economical use. 



I 1 8 IN DIC A TOR PR A CTICE. 

The only other faults of the diagrams are too little 
compression to insure smooth running, and — if it is a 
fault — a slight lack of lead. 

To insure proper action in a governor, the fly-wheel 
must be of sufficient weight to allow the crank to pass 
the centres where steam has no effect in moving the 
piston, without sensible decrease in the speed ; also, 
to allow diminution of pressure during the stroke by 
initial expansion without a reduction of speed sufficient 
to induce over-action of the governor. A few pounds 
of metal in the fly-wheel often results in a large saving 
of steam. 






DIAGRAMS FROM LOCOMOTIVE-ENGINES. 1 IQ 






CHAPTER XV. 

DIAGRAMS FROM LOCOMOTIVE-ENGINES. 

HOW TO CONNECT THE INDICATOR. 

BUT little attention, comparatively, has been given 
to indicating locomotive-engines. At first thought it 
may seem somewhat difficult to get diagrams from a 
locomotive swinging along at 60 miles an hour, but if 
suitable preparations are made there is nothing worth 
the name of difficulty in doing it. It will be found 
advisable to pipe the two ends of the cylinder together, 
using one indicator. The holes should be drilled in 
the outer side of cylinder, at the centre, up and down, 
for f-inch pipe, the pipe connecting to a three way 
cock at the centre, in which the indicator-cock is 
screwed ; the pipe should be kept as close to the 
cylinder as practicable. Thus arranged, the indicator 
will stand at the centre of the cylinder lengthwise, and 
near the bottom of the steam-chest. 

DRUM-MOTION. 

The drum-motion may be had by using the arrange- 
ment of lever shown in Fig. 31, which is essentially 
the same as that shown in Fig. 1. The reducing-lever 
and connection should be made of steel, with thimbles 
made fast in the ends so as to provide bearings not 
less than \ inch in diameter, and about 1^ inches in 



120 



INDICATOR PRACTICE. 




DIAGRAMS FROM LOCOMOTIVE-ENGINES. 121 

length. The upper end of the lever swings on a pin 
made fast in an angle-iron bolted to the running-board, 
and the outer end of the connection journals on a stud 
screwed in the cross-head : this stud must be long 
enough to carry the lever so far out that the cord will 




Fig. 32 — Scale 60. 

4 miles per hour. Reverse-lever in 7th notch. Throttle open. Grade 47^ feet per 

mile. 



lead direct to the indicator in a straight line fore and 
aft. 

Any other suitable arrangement with which no guide- 
pulleys are employed may be used instead of this, but 
the one shown will generally be found a convenient 



one. 



122 



INDICATOR PRACTICE. 



SAFETY PRECAUTIONS. 



A place must be boxed up, the box being securely 
bolted to the bumper and cylinder, or other parts, in 
which to sit while taking the diagrams. The outside 
and front of this box should be so high as to prevent 




Fig. 33— Scale 60. 

8.30 miles per hour. Reverse-lever in 5th notch. Throttle open. Grade 36 feet 

per mile. 



the possibility of the operator being thrown out by a 
lurch of the engine ; both hands are fully employed in 
handling the indicator, and the attention is concen- 
trated on the operation, so no thought about safety 
should be necessary. With these precautions diagrams 



DIAGRAMS FROM LOCOMOTIVE-ENGINES. 1 23 

may be taken about as comfortably from a locomotive 
as from a stationary engine at the same speed. 

HOW TO PRESERVE THE DATA. 

The operator can note the necessary data on the dia- 
grams as he takes them, but it is inconvenient for him to 




11.06 miles per 



Fig. 34— Scale 60. 

hour. Reverse-lever in 4th notch. Throttle two thirds open. 
Grade 47^ feet per mile. 



do so. It is better that he have an assistant, and arrange 
as follows: Number as many blanks as will be required, 
from one upward, and arrange them in a package con- 
venient to be come at in the order of the numbers. 
The assistant takes his place in the cab, provided with 
a book in which are written numbers corresponding to 



124 



INDICATOR PRACTICE. 



those on the indicator-blanks. The operator begins 
with No. i blank, and when the assistant observes him 
remove it from the drum, he enters against I in his 
book the steam-pressure, positions of throttle and re- 
verse levers, speed and location on the road. This 
is repeated with No. 2, and so on. Some of the dia- 




Fig. 35— Scale 60. 

15.49 miles per hour. Reverse-lever in 3d notch. Throttle open. Grade 42 feet 

per mile. 

grams may be worthless, but the entries will have been 
made the same, and if the assistant watches the opera- 
tor his entries will tally correctly with the numbers on 
the diagram. 

Exactly the same reasoning that applies to diagrams 
from other engines applies to those from locomotives. 



DIAGRAMS FROM LOCOMOTIVE-ENGINES. 1 25 

From the character of the valve-motion compression 
will be high at short cut-off, and back-pressure at high 
speed" will be what in stationary-engine practice would 
be considered excessive. Owing to high compression, 
clearance cannot be satisfactorily reduced so low as it 




Fig. 36 — Scale 60. 

34.31 miles per hour. Reverse-lever in 2d notch. Throttle open. Grade 42 feet 

per mile. 

otherwise could be. Compression should never ex- 
ceed steam-chest pressure at the shortest cut-off. 



DIAGRAMS REPRESENTING GOOD PRACTICE. 

The diagrams 32 to 37, inclusive, represent good 
American practice in the way of steam-distribution in 
locomotive-cylinders. They were taken from a loco- 
motive running on freight-service. The cylinders are 



126 INDICATOR PRACTICE. 

i8 // X24 // , steam-ports I.#')ki6", full travel of valve 5 
inches, outside lap of valve -J inch, inside lap -J inch, 
lead at full stroke T y inch. The driving-wheels (out- 
side of tires) are 62 inches diameter. The weight of 
train, including tender, was 1,301,700 pounds. 

The back-pressure on all these diagrams is low for 




Fig. 37— Scale 60. 
14.75 miles per hour. Reverse-lever in ist notch. Throttle open. Grade 30 feet 

per mile. 

locomotive practice, and the mean effective pressure 
for the different grades of expansion is high ; Fig. 32 
is noticeable for showing remarkably high mean effec- 
tive pressure. The work done in the two ends of the 
cylinder is very nearly equal. As representing good 
valve-setting, these diagrams may serve as models ; they 
are seldom equalled in this respect. 



DIAGRAMS FROM LOCOMOTIVE-ENGINES. 1 27 






It will be observed at short cut-off that the initial 
pressure is not nearly so well maintained up to cut-off 
as in stationary engines ; but in cylinders so much ex- 




posed as locomotive-cylinders are, some wire-drawing, 
which results in slight superheating, is not objection- 
able. The cylinders, for obvious reasons, are large for 



128 INDICATOR PRACTICE. 

the work at high speeds, and some reduction in initial 
pressure and high compression avoids what would 
otherwise be too low terminal pressure. By increasing 
compression more steam is saved by earlier exhaust- 
closure ; hence the saving in this way balances the ap- 
parent loss from high terminal pressure due to in- 
creased compression. 

TOO MUCH COMPRESSION. 

Fig. 38 represents a pair of diagrams from a passen- 
ger-locomotive working at short cut-off. Compression 
is carried too far. In such a case loss is likely to occur 
from a springing up of the edge of the valve, permit- 
ting steam to blow through into the exhaust. The 
tendency is also to wear the valve in such shape that 
it will leak. If so short cut-off is to be employed, 
there should be more clearance. With a little later 
cut-off exhaust-closure would be delayed, and then the 
clearance would be sufficient. 

It cannot be known except by trial with the indica- 
tor what the effect of a given clearance will be so far 
as concerns compression. Compression will seldom 
be as high as would appear from calculation owing to 
heat being rapidly taken up to warm the exposed sur- 
faces of the cylinder. At high-speed compression will 
be higher than at low-speed, because there is less time 
for the transfer of heat, and because back-pressure is 
generally higher at high-speed. 

MODERATE AND HIGH SPEED COMPARED. 

Diagrams 39 and 40 were taken from a locomotive 
with cylinders i6 /; X24", steam -ports ii"Xi4", full 






DIAGRAMS FROM LOCOMOTIVE-ENGINES. 



129 



travel of valve 4^ inches, outside lap f inch, lead T ^ 



inch to \ 



inch. The driving-wheels were 60 inches 



diameter. Fig. 39 was taken at a speed of 35 miles 










per hour, the engine hauling a light train ; 40 was 
taken at a speed of 60 miles per hour, engine running 
light. The two speeds correspond to piston-speeds of 
9 



13° 



INDICATOR PRACTICE. 



784 and 1344 feet per minute, respectively; boiler- 
pressure in both instances 125 pounds. 




C/) 
I 



The effect of the higher speed is plainly seen in 
the reduced area of 40 ; but with ports so small for 
such piston -speed the reduction of area is less than 






DIAGRAMS FROM LOCOMOTIVE ENGINES. 13 I 

would be expected. If it were not for compression 
there would undoubtedly be much greater difference 
between the diagrams. Compression in 40 is ac- 
countable for the close approximation to boiler-pres- 
sure, and this high pressure at the beginning helps in 
keeping the pressure up to the end of the stroke. 
Both diagrams show a good deal of falling off in pres- 
sure — initial expansion— before cut-off, and this is of 
course the greatest at the higher speed — that is, in 
40. The back- pressure is also somewhat higher in 
40. In both 39 and 40 the back-pressure increases 
as the opening for exhaust gradually narrows, so 
much so that it cannot be told from either diagram 
where exhaust-closure took place. This increase in 
back-pressure before exhaust-closure is greater in 40 
than in 39, owing to the higher speed. 

In calculating loss from back-pressure it should be 
reckoned up to the point of exhaust-closure only; 
after that the steam present is saved for further use. 
But as increase of pressure at the time of exhaust- 
closure increases the pressure at the end of compres- 
sion, and as at this point it should not be greater than 
steam-chest pressure, it follows that if there were never 
more than 3 or 4 instead of 10 or 15 pounds pressure 
(above atmosphere) when the exhaust closed, clear- 
ance might be less. 

ECONOMY OF THE LINK-MOTION. 

The diagram in full lines, Fig. 41, is from a locomo- 
tive-engine with cylinders i6' / X22 // , at a speed of 248 
revolutions, or a piston-speed of 909 feet, per minute. 
This diagram is interesting as compared with those 



132 



INDICATOR PRACTICE. 



taken with other forms of cut-off, since it is quite gen- 
erally held to be a fact that the link is very inefficient 




as a means of working steam expansively, the loss as 
compared with other means of steam - distribution 
being variously estimated at from 25 to 40 per cent. 



DIAGRAMS FROM LOCOMOTIVE-ENGINES. I 33 

In order more clearly to make this comparison, a 
hypothetical diagram has been plotted in dotted lines, 
which, I believe, will be accounted a very good one 
indeed for an automatic cut-off engine at that piston- 
speed. 

The important points of loss in the distribution of 
steam by the link-motion are claimed to be : A failure 
to approximate boiler- pressure in the cylinder; too 
early release ; excessive back-pressure ; too early ex- 
haust-closure, and excessive clearance, the last in part 
being necessary to avoid too high compression incident 
to early exhaust - closure. When this diagram was 
taken the boiler-pressure was 128 pounds, and the cut- 
off at 8^ inches. The initial pressure is about 14 
pounds less than boiler-pressure. 

Of this it may here be remarked, that the highest 
point reached by the pencil does not at high speed and 
sharp lead, represent initial pressure in the cylinder, but 
rather the inertia of the reciprocating parts of the in- 
dicator, which always under such circumstances carries 
the pencil higher than is due to the steam pressure in 
the cylinder. 

Besides the lack of boiler-pressure in the cylinder 
there is a fall of pressure (initial expansion) of 19 
pounds before cut-off. This lack of pressure at the 
beginning of the stroke and fall of pressure before cut- 
off represent loss to some extent, although, as previ- 
ously said, all is not loss that appears to be. There is 
no evidence of material loss from too early release, and 
there is none too much compression for the amount of 
clearance-space. The line of counter-pressure shows 
the back-pressure to be about 6 pounds. The loss 



134 INDICATOR PRACTICE. 

from this is apparent, but is modified by early exhaust- 
closure. Some saving would result from reducing the 
clearance and compression — that is, if both were re- 
duced. 

Comparing the actual with the hypothetical diagram, 
the efficiency of the latter over the former is between 
14 and 15 per cent, not 25 or 40 per cent. That is, 
assuming that the clearance, 7^- per cent, as repre- 
sented by the full clearance-line, could with safety be 
reduced one half, as represented by the dotted clear- 
ance-line ; that the back-pressure may be less than 2 
pounds, and that as good steam-line as that shown in 
the dotted diagram may be had, the dry steam ex- 
hausted would be 20 pounds per hour for the actual, 
and a little more than 17 for the hypothetical, dia- 
gram. This would not be all gain, as the somewhat 
greater extremes of temperature in the cylinder in the 
instance of the hypothetical diagram would result in 
correspondingly greater condensation, and hence loss. 

It is customary with those who condemn the link- 
motion to stop here and charge all this loss of effi- 
ciency to it. As a matter of fact, the link is responsible 
for only a very small part of it. To appreciate this it 
is only necessary to look at another condition that 
equally with the valve-motion influences the steam- 
distribution, viz., the dimensions of ports. In this case 
the steam-ports are iJ^Xh", in area between y^th 
and ^th that of the piston. In the best stationary- 
engine practice, with which it is the custom to com- 
pare the link-motion, this proportion would not be ac- 
cepted for a piston-speed much greater than one half 
that at which this diagram was taken ; and to produce 






DIAGRAMS FROM LOCOMOTIVE-ENGINES. 1 35 

a diagram equal to the one sketched for comparison 
from a modern automatic cut-off stationary engine, the 
area of ports would need to be nearly double what it is 
in this case. If the area of the ports is increased as in- 
dicated, and the link-motion used, the most of this dif- 
ference against it will disappear. The opinion that 
small ports are a part of the link-motion, or at least that 
they are a necessity when the link is used, although 
entirely without foundation, is almost universal. By 
balancing or relieving the valve of pressure, as is done 
in stationary-engine practice, there is no more objec- 
tion to large ports in one instance than in the other. 

With regard to the 6 pounds back-pressure, the out- 
side lap of valve is f inch, inside lap o ; hence the area 
of port-opening for exhaust at the beginning of the 
return-stroke is not less than n square inches, while 
all the steam exhausted must pass through a nozzle hav- 
ing an area of only 5 square inches, something not al- 
ways considered in discussing the efficiency of the link- 
motion. 

The diagram shows, so far as a diagram from the 
link-motion at a single point of cut-off and from one 
end of the cylinder can show, very correct valve-setting. 
Compression cannot well be carried higher, because it 
is necessary to provide for shorter cut-off, in which the 
exhaust-closure will be earlier. 

STEAM-CONSUMPTION MEASURED FROM A LOCOMOTIVE- 
DIAGRAM. 

Fig. 42 illustrates the calculation of the steam-con- 
sumption from a locomotive -diagram according to 
Thompson's table. Measuring the mean effective 



136 



INDICATOR PRACTICE. 



pressure, it is found to be 36.25 pounds, and the ter- 
minal pressure above vacuum is 31.2. In the table 
against 31 and under 2 is the number 1062.859. This 
number divided by 36.25 gives 29.3, the steam -con- 
sumption uncorrected for clearance and compression. 




Fig. 42— Scale 50. 



The length of line tE is 2.3 inches, and of tC 3.2 
inches ; hence 

29.3 X 2.3 



3.2 



21, 



the pounds of dry steam exhausted per horse-power per 
hour. Assuming the water present to have been 20 
per cent of the steam, the water-consumption per 



DIAGRAMS FROM LOCOMOTIVE-ENGINES. I 3,7 

horse-power per hour would be about 25J pounds. 
This diagram is not used because it is a particularly- 
good one so far as economy is concerned, but because 
it happens to be a good one for the purpose for which 
it is wanted. 

FINDING THE HORSE-POWER. 

In computing the horse power from locomotive-dia- 
grams it is convenient to find a constant multiplier for 
one pound mean effective pressure and one revolution 
per minute ; then the mean effective pressure multi- 
plied by the revolutions per minute and by this con- 
stant multiplier will give the horse-power of any dia- 
gram. Thus, say the area of piston is 250 inches, and 
the stroke 24 inches : each revolution gives 4 feet pis- 
ton-travel, and a constant multiplier for ore cylinder 
of that engine is 

250 X 1 X 4 

= .0303. 

33000 J J 

Suppose the revolutions per minute when a particular 
diagram was taken to have been 200, and the mean 
effective pressure of the diagram 60 pounds, then 
200 X 60 X .0303 = 363.6, the horse -power of one 
cylinder. 

THE EFFECT ON THE DIAGRAM OF THE STEAM-DISTRIBU- 
TION PECULIAR TO THE LOCOMOTIVE. 

An inspection of any of the diagrams from locomo- 
tives taken at short cut-off illustrates why it is com- 
paratively easy to get such diagrams at high speeds. 
At high speed cut-off is short, and compression begins 



I38 INDICATOR PRACTICE. 

early in the return-stroke, previous to which the back- 
pressure is somewhat increased by the gradual narrow- 
ing up of the port-opening. The pencil and other 
reciprocating parts of the indicator are thus gradually 
started upward, and occupy considerable time in get- 
ting to their highest position. At the same speed in 
an engine in which exhaust-closure does not occur 
until near the end of the return-stroke the pencil is 
forced more nearly instantly to its highest position, 
and the inertia of the reciprocating parts of the indica- 
tor plays an important part in distorting the diagram. 

Cut-off in the locomotive at high speed is also gra- 
dual, and the decrease of pressure previous to cut-off 
is considerable, so the fall of the pencil is gradual 
rather than abrupt. If the attempt were made to get 
a diagram from an engine in which the steam-distribu- 
tion was like that represented in Figs. 10 or 22, at a 
speed corresponding to 60 miles an hour with the 
locomotive, considerable trouble would be experienced. 



OTHER USES OF THE INDICATOR. 1 39 



CHAPTER XVI. 
OTHER USES OE THE INDICATOR. 

STEAM-CHEST DIAGRAMS. 

THUS far the indicator has been considered in iti 
application to the cylinder of the steam-engine. It is 
equally applicable to the cylinders of air and gas en- 
gines, or to any purpose where quickly varying fluid- 
pressure is to be recorded. In connection with the 
steam-engine its application to the st^am-pipe or steam- 
chest is frequently important. If upon applying the 
indicator to the cylinder of a steam-engine it is found 
that there is a material loss of pressure between the 
boiler and cylinder, it is desirable to know what is re- 
sponsible for this loss. The stricture may be in the 
ports, or it may be in the steam-pipe. If the indicator 
is applied to the steam-chest, motion being had the 
same as when it is used on the cylinder, it will show 
what the pressure is there during the stroke of the pis- 
ton, and by comparison how much of the loss of pres- 
sure is due to the effort of the steam in getting through 
the ports. 

A diagram something like 43 may be expected from 
the steam-chest. This diagram was taken from the 
steam-chest of an automatic engine with boiler-pres- 
sure 75 pounds, represented by B. When the valve 



140 



INDICATOR PRACTICE. 



opens for admission the pressure suddenly falls to C 9 
about 2 pounds. Steam is cut off at D y from which 
point the pressure rises very quickly to £, 2 pounds 
higher than boiler-pressure. It seemed at first that 










this rise of pressure higher than that in the boiler was 
not probable, and a test was made of the indicator and 
steam-gauge; they were found to agree exactly. It 
then appeared evident that the rapid flow of steam to 



OTHER USES OF THE INDICATOR. 14* 

the steam-chest while steam was being admitted to the 
cylinder could not be instantly checked, and did not 
cease until the pressure was increased by 2 pounds.* 

DIAGRAMS FROM PUMPS. 

The indicator has been of great advantage in bring- 
ing about improvements in the construction of pump- 
cylinders, especially in those for water-works, or for 
handling large quantities of water. The nearer the 
diagram from a pump is to a rectangle the better prac- 
tice it represents. Fig. 44 shows all that can be de- 
sired in this respect. The distance from the atmos- 
pheric line to the lower line represents the suction, 
greater or less according to the height the water is 
lifted and to the freedom with which it passes to the 
pump. The upper line represents the pressure against 
the plunger or piston in forcing the water out ; this 
pressure is due to the height to which the water is 
forced and the friction it encounters. 

Beginning with the right-hand lower corner of the 
diagram, the cylinder being full of water, the pressure 
rises, as soon as the motion of the plunger begins, to 
87 pounds above atmosphere, and continues constant 
to the end of the stroke, showing that there was no 
shock due to starting the water-column, and that the 
passage of the water from the pump-cylinder was prac- 
tically without resistance. At the very beginning of 
the return stroke the pressure instantly fell to about 8 
pounds below atmosphere, the degree of vacuum re- 

*Mr. Charles T. Porter was, so far as the writer knows, the first 
to call attention to this somewhat curious but entirely natural be- 
havior of steam in the steam-chest. 



142 INDICATOR PRACTICE. 

quired to lift the water. The lower or suction-line is 




as regular as the upper or discharge-line, showing with 
what freedom the water passed the suction-valves. 



OTHER USES OF THE INDICATOR. 



H3 



Such a diagram as this shows an absence of shock to 
the pump, and that a cylinder full of water is handled. 
In contradistinction to this diagram, diagrams are 
often taken from pumps that show enormous shocks 







to the parts, and only partial filling of the cylinder. 
Fig. 45 is a fair specimen of what should be avoided. 
It represents ancient and some modern practice. 

If the lines of a pump diagram enclose a rectangular 



144 INDICATOR PRACTICE. 

figure, it may be assumed that the working of the 
pump is satisfactory. If there is undue friction of the 
water in getting into or out of the cylinder it will be 
greater at some parts of the stroke than at others, and 
this will be shown by corresponding inclinations of the 
suction and discharge-lines. If the cylinder is not 
filled with water, the line, as at the right in Fig. 44, 
will not be vertical. Shocks and jars and intermittent 
action will be shown by abrupt irregularities in the 
lines, as in Fig. 45. 



STEAM-ENGINE ECONOMY. 14$ 



CHAPTER XVII. 
STEAM-ENGINE ECONOMY. 

GENERAL CONSIDERATIONS. 

STEAM-ENGINE economy in a broad sense involves 
considerations of construction and design, as well as 
everything that enters into cost of maintenance and 
operation. With the engineer in charge of engines 
and boilers, however, the problem is ordinarily that of 
getting the best possible results from machinery al- 
ready constructed and placed in his charge. An im- 
portant part of his education is in the direction of how 
best to accomplish this end, and the value of his ser- 
vices is largely dependent upon his ability in this 
direction. Economy to him means keeping down the 
fuel account, having small bills for repairs, little or no 
loss from enforced stoppages, maintaining regular 
speed, and having the least possible loss from de. 
terioration. 

The cost of fuel is always an important matter, but 
sometimes it is of more importance that there be no 
enforced stoppages, or that the speed be very regular. 
The engineer must study this in any particular in- 
stance, and govern himself according to circumstances. 
10 



146 INDICATOR PRACTICE. 



UNDERLOADED ENGINES. 

So far as the use of fuel goes, an engineer often finds 
himself confronted with conditions that render the at- 
taining of good economy impossible. The only course 
then is to make the best of bad surroundings. The 
condition unfavorable to fuel economy most likely to 
be met with is an engine too large for its work. In a 
non-condensing engine the useless work of moving the 
piston against the pressure of the atmosphere must 
always be done. The resistance the piston meets with 
from the atmosphere being, in round numbers, 15 
pounds per square inch, if the mean effective pres- 
sure required to do the work is but 15 pounds, then as 
much work is done in overcoming the atmospheric 
resistance as is done in overcoming the friction of the 
parts and doing the useful work. If the load is in- 
creased so that the mean effective pressure is 45 
pounds, only one third as much work is done against 
the atmosphere as against the other resistances. One 
reason, then, and a very important one, why an under- 
loaded engine works with poor economy is that the 
useless work is too large a fraction of the total work 
done by the steam. So far only the useless work of 
overcoming the resistance of the atmosphere has been 
referred to. There will be, besides this, some further 
back-pressure which will not increase in proportion as 
the mean effective pressure is increased, and this, so 
far as it goes, strengthens the reason just given. 

In a condensing-engine the piston has always to be 
moved against pressure due to imperfect vacuum, and 



STEAM-ENGINE ECONOMY. I47 

some back-pressure besides, so the same reason holds 
good, but not to the same extent. 

Another reason why poor economy and light loads 
go together is that part of the work done in the cylin- 
der of a steam engine is done to overcome friction of 
moving parts, and this friction does not increase as 
fast as the load is increased ; it is sometimes nearly as 
great with no load as with the engine fairly loaded. 

A third reason, which has been previously briefly 
referred to, is condensation of steam in the cylinder. 
When ordinary dry steam from the boiler enters the 
cylinder, cooled by the low temperature during expan- 
sion and exhaust, a very material portion of it is con- 
densed, parting with its latent heat to bring up the 
temperature of the exposed surfaces. In an engine 
lightly loaded the steam thus condensed is a larger 
fraction of the total steam used than in one more heavily 
loaded. The exact loss from condensation cannot 
from present knowledge of the subject be calculated, 
or very closely approximated, so that it cannot be told 
by calculation just what the mean effective pressure on 
an engine should be for the best economy in fuel-con- 
sumption. Experimentally it has been found that 
with steam from 70 to go pounds, by gauge, the best 
economy in a non -condensing engine obtains when 
the load is such that cut-off will be not much, if any, 
earlier than one-quarter stroke. With this cut-off the 
terminal pressure will be from 5 to 10 pounds above 
atmosphere. At lower steam-pressure than named the 
cut-off should be still later. With condensing engines 
the cut-off may be such that the terminal pressure will 
be at atmosphere, or a little below. 



I48 INDICATOR PRACTICE. 

But the engineer has to do with the engine under- 
loaded, — too large for the work, — and must consider 
how he can keep the coal-consumption down without 
loss in some other direction. When the cut-off is ma- 
terially before quarter-stroke, so much so that the ter- 
minal pressure in a non-condensing engine is below 
atmosphere, it is in the interest of economy to reduce 
the speed. This is not, however, always practicable. 
Sometimes the construction of the engine is such that 
a change of speed will disarrange the governor to such 
an extent that the regulation will be poor ; in other 
instances it is merely a matter, so far as the governor 
is concerned, of a change of a pulley. 

Another important consideration in a proposed re- 
duction of speed is the weight of fly-wheel. Good 
regulation cannot be had with a fly-wheel too light for 
the work. If the fly-wheel is only of sufficient weight 
for the speed as it is, if the speed is reduced it will be 
too light. The momentum of a fly-wheel varies as the 
diameter and as the square of its revolutions ; hence, 
reducing the speed decreases its capacity rapidly. 
There are several rules for determining the proper 
weight of a fly-wheel, the following of which is perhaps 
as simple as any : 

Rule for finding the weight of the rim of a fly-wheel 
for an automatic engine. Multiply 6,000,000 by the in- 
dicated horse-power of the engine, and divide the pro- 
duct by the diameter of the wheel in feet multiplied 
by the square of its number of revolutions per minute. 

Take, for example, an engine developing 75 indi- 
cated horse-power, having a fly-wheel pulley 14 feet 
diameter, running 80 revolutions per minute : what 






STEAM-ENGINE ECONOMY. 1 49 

should be the weight of metal in the rim of the wheel? 
6,000,000 X 75 = 450,000,000 ; the square of 80 is 80 X 
80 = 6400, and 6400 X 14 = 89,600. Then 450,000,000 
-r- 89,600 = 5022 pounds for the weight of the rim of 
the wheel. 

Some builders use a larger constant than 6,000,000, 
which gives greater weight of wheel, but more use a 
smaller constant. The rule, as given above, gives very- 
regular turning, and may be safely employed by the 
engineer. Cast-iron weighs about .26 pound per cubic 
inch ; so by finding the cubic inches in the rim of the 
wheel, and multiplying by this decimal (.26), the weight 
will be found with reasonable exactness ; then finding 
by the use of the indicator the horse-power developed, 
it can be told whether the speed can be decreased with 
satisfactory results without increasing the weight of 
wheel. For full-stroke engines a wheel of three fourths 
the weight, as above found, will generally answer the 
requirements. The diameter of the wheel may, if a 
fly-wheel pulley is used, be measured from the outside. 
Where a square-rimmed wheel is used the diameter 
should be measured from the centre of the rim, so as 
to get the mean of the outside and inside diameters. 

In some instances, where close regulation and even 
turning are not very essential, the speed may be re- 
duced so as to bring the fly-wheel proportion con- 
siderably less than found by the rule given. Judg- 
ment must be used in considering this. In other in- 
stances a plain fly-wheel may be placed beside the fly- 
wheel pulley. 



150 INDICATOR PRACTICE. 

WORKING WITH LOWER STEAM PRESSURE. 

Reducing the speed is usually the only practical 
means of increasing the economy of fuel-consumption 
in an underloaded non-condensing engine. By this 
means the useless work done against the pressure of 
the atmosphere is diminished, the inevitable loss from 
filling the clearance-space with steam at every stroke is 
less, because the number of times this space is filled, 
per minute or per hour, is less, and friction is generally 
reduced. A slight saving may sometimes be effected 
by working with reduced steam-pressure ; but what it 
will amount to, if anything, can only be told by trial. 
It will depend upon the steaming qualities of the boiler 
under the higher and the lower pressures ; upon the 
construction of the engine, particularly as to whether 
the valves work under full pressure or are wholly or 
partially balanced ; upon whether leakage will be less 
at low-pressure ; and upon a variety of conditions that 
cannot well be enumerated. Usually in a well-con- 
structed engine, unless expansion is considerably — say 
2 or 3 pounds at least — below the atmosphere, work- 
ing with lower boiler-pressure will not decrease the 
coal-consumption. If advisable to reduce the initial 
pressure, better results will usually follow a small 
amount of throttling, keeping the boiler-pressure as it 
is. Reducing the boiler-pressure in the instance of an 
underloaded condensing-engine is much more likely to 
save fuel than in one worked non-condensing. In any 
case, as previously intimated, the effect can only be 
known by trial. Weighing the coal used running both 
ways will settle the matter conclusively. 



STEAM-ENGINE ECONOMY, I 5 I 



OVERLOADED ENGINES. 

If an engine is overloaded the remedy that most na- 
turally suggests itself is to increase the speed. The 
diagram will show, by the freedom with which the 
steam gets into and out of the cylinder, whether in this 
respect higher speed is advisable, or will accomplish 
the end sought. If initial pressure is nearly equal to 
boiler-pressure, with only a pound or two of back-pres- 
sure, then there will be no trouble in increasing the 
speed from 10 to 20 per cent, if the wearing and moving 
parts can be run faster without danger or inconveni- 
ence. If the diagram shows that the steam-passages 
are small for the present speed, then but little will be 
gained in the way of additional power by increasing 
the speed, while there may be a loss in economy of 
fuel. Increasing the speed of an engine ought to im- 
prove the regulation, because it increases the capacity 
of the fly-wheel. 

WORKING WITH HIGHER STEAM-PRESSURE. 

Frequently the very best remedy for an overloaded 
engine is increasing the steam-pressure. Doing this 
of course involves previous considerations of the 
strength of the boiler, and of various parts of the 
engine, as well as the amplitude of the wearing sur- 
faces to resist the higher pressure. When there are 
no objections to increasing the pressure, doing so gen- 
efally increases economy, for reasons previously ex- 
plained. 

ADDING A CONDENSER. 

Another plan for helping out an overloaded non- 



152 INDICATOR PRACTICE. 

condensing engine is to add a condenser. Where fairly 
high pressure of steam is carried — say, not less than 75 
pounds gauge-pressure — and the cut-off is from one- 
quarter to one-third stroke, a condenser will, by add- 
ing from 9 to 11 pounds pressure below atmosphere, 
shorten the cut-off, and the economy will be increased. 
Adding a condenser to a lightly-loaded engine working 
with high steam-pressure, in the expectation of saving 
coal, as is frequently done, will generally end in disap- 
pointment. Condensation in the cylinder will be in- 
increased, and colder feed must be used, the two fre- 
quently neutralizing all that is otherwise gained by the 
use of the condenser. 

When, from any cause, it is necessary to materially 
reduce the steam-pressure carried, thus in effect mak- 
ing the engine small for the work, then a condenser is 
a valuable addition. 

HEATING FEED-WATER. 

In a non-condensing engine advantage should always 
be taken of heating the feed-water by the exhaust- 
steam. In this way a saving of coal equal to from 10 to 
15 per cent will be effected, besides which it is much 
better for the boiler to feed hot water. With a con- 
densing-engine there is very little gain from the use of 
a heater, provided the temperature of the hot-well is 
not unnecessarily low. 



TABLES. 



153 



CHAPTER XVIII. 



TABLES. 



TABLE I. 
Areas of Circles in Square Inches. 



Diameter Are 


a in square 


Diameter 


Area in square 


Diameter 


AreaJajsquare 


in inches. 


inches. 


in inches. 


inches. 


in inches. 


inches. 


A 


OOOig2 


iH 


2.2365 


44" 


18.666 


1 

30 


OO0767 


if 


2.4053 


5 


19.635 


tV 


OO3068 


lit 


2.5S0I 


54 


20.629 


4 


OI2272 


13 


2.7612 


54 


21.648 


A 


02761 


x 16 


2.9483 


5f 


22.69I 


i 


04908 


2 


3.1416 


54 


23.758 


A 


07670 


2i 


3.5466 


54 


24.851 


1 


I IO45 


2i 


3.9761 


5* 


25.967 


A 


15033 


2f 


4430I 


54 


27.IO9 


i 


1035 


2| 


4.9087 


6 


28.274 


A 


24851 


2| 


5.4II9 


64 


29.465 


1 


30680 


2f 


5.9396 


64 


30.679 


11 


37122 


2| 


6.4918 


6| 


31.919 


f 


44179 


3 


7.0686 


64 


33.183 


if 


51849 


34 


7 . 6699 


64 


34-472 


£ 


60132 


34 


8.2958 


6* 


35.785 


if 


69029 


3f 


8 . 9462 


64 


37.122 




7854 


3* 


9.6211 


7 


38.485 


T ] 


88664 


34 


10.3210 


74 


39-871 


li 


99402 


31 


11.0447 


74 


41.283 


'A 1 


1075 


3| 


11.7933 . 


71 


42.718 


ii 1 


2272 


4 


12.566 


74 


44.179 


iA 1 


3530 


44 


13.364 


74 


45.664 


if 1 


4849 


44 


14.186 


7f 


47-173 


1* r 


6229 


41 


15.033 


74 


48.707 


ii 1 


7671 


44 


15.904 


8 


50.266 


iA 1 


9175 


4f 


16 800 


84 


51.849 


if 2 

1 


0739 


4f 


17.721 


84 


53.456 



154 



INDICATOR PRACTICE. 
TABLE I.— Continued. 



Diameter 


Area in square 


Diameter 


Area. in square 


Diameter 


Area in square 


in inchts. 


inches. 


in inches. 


inches. 


in inches. 


inches. 


8f 


55-088 


I3f 


148.490 


I9i 


287.272 


84 


56.745 


13* 


151. 20I 


I9i 


29I.040 


81 


58.426 


14 


153.938 


I9l 


294.832 


8f 


60. 132 


I4i 


156.700 


194 


298.648 


8J 


61.862 


I4i 


159.485 


19! 


302.489 


9 


63.617 


I4l 


162.296 


19! 


306.355 


9* 


65.397 


I4i 


165.130 


194 


310.245 


9i 


67.201 


I4l 


167.990 


20 


314.16 


9* 


69.029 


14* 


170.874 


20i 


318.IO 


94 


70.882 


I4i 


173.782 


20j 


322.06 


9* 


72.760 


15 


176.715 


20f 


326.05 


9t 


74.662 


15* 


179.673 


20| 


330.06 


9* 


76.589 


I5i 


182.655 


20f 


334-IO 


IO 


78.540 


i5l 


185.660 


20f 


338.16 


ioi 


80.516 


i5i 


188.692 


204 


342.25 


ioi 


82.516 


I5f 


191.748 


21 


346.36 


iof 


84.541 


151 


194.828 


214 


350.50 


io£ 


86.590 


I5l 


197.933 


2li 


354-66 


iof 


88.664 


16 


201.062 


2 If 


358.84 


iof 


90.763 


16J 


204.216 


2li 


363-05 


io| 


92.886 


i6i 


207.395 


21* 


367.28 


II 


95.033 


i6| 


210.598 


2lf 


37L54 


II* 


97.205 


i6| 


213.825 


21* 


375.83 


Hi 


99 . 402 


i6f 


217.077 


22 


380.13 


III 


IOI.623 


i6f 


220.354 


224 


384.47 


Hi 


IO3.869 


16* 


223.655 


224 


388.82 


I If 


106.139 


17 


226.981 


22f 


393.20 


Hf 


108.434 


174 


230.331 


22i 


397-61 


II* 


IIO.754 


i7i 


233 • 706 


22f 


402 . 04 


12 


113 098 


1 71 


237.IO5 


22f 


406 . 49 


12* 


II5.467 


i7i 


240 529 


224 


410.97 


I2i 


H7.859 


17* 


243 977 


23 


415.48 


I2| 


120.277 


1 71 


247.450 


234 


420.OO 


I2i 


122.719 


174 


250.948 


234 


424.56 


I2| 


125.185 


18 


254.470 


23* 


429.13 


I2f 


127.677 


184 


258.016 


234 


433-74 


12* 


130.192 


18* 


261.587 


234 


438.36 


13 


132.733 


18* 


265.183 


23* 


443.OI 


I3i 


135.297 


184 


268.803 


234 


447.69 


I3i 


137.887 


18* 


272.448 


24 


452.39 


I3l 


140.501 


1 8| 


276.117 


244 


457.II 


134 


143 139 


1 84 


279.811 


24i 


461.86 


13* 


145.802 


19 


283.529 


24* 


466 . 64 



TABLES. 
TABLE \.— Continued. 



155 



Diameter 


Area in square 


' Diameter 


Area in square 


Diameter 


Area in square 


in inches. 


inches. 


in inches. 


inches. 


in inches. 


inches. 


2 4 i 


47144 


29J 


700.98 


35i 


975-91 


24l 


476.26 


30 


706.86 


35l 


982.84 


24f 


481. II 


3o£ 


712.76 


35! 


989.80 


24i 


485. 9S 


3oi 


718.69 


35f 


996.78 


25 


490.87 


3of 


724.64 


35i 


1003 . 79 


25i 


495 • 80 


3o£ 


730.62 


35! 


IOIO.82 


25i 


500.74 


3of 


736.62 


36 


1017.88 


25l 


505.71 


3of 


742.64 


36£ 


1024.96 


25i 


5TO.71 


30| 


748.69 


36f 


1032.06 


25I 


515.73 


3i 


754-77 


36f 


IO39 • 19 


25i 


520.78 


3ii 


760.87 


36£ 


IO46.35 


25i 


525.84 


3ii 


766.99 


36f 


1053-53 


26 


530.93 


3*f 


773.14 


36f 


1060.73 


26i 


536-05 


3i* 


779.31 


36J 


1067.96 


26i 


541.19 


3 if 


785.51 


37 


1075.21 


26J- 


546.36 


3if 


791-73 


37i 


1082.50 


26i 


55L55 


3'i* 


797.98 


37i 


1089.79 


26f 


556.76 


32 


804.25 


371 


IO97. II 


26f 


562.00 


32i 


810.54 


37i 


II04.47 


26| 


567.27 


32i 


816.86 


37* 


II I I. 84 


27 


572 56 


32f 


823.21 


37* 


I II9.24 


27i 


577.87 


32i 


829.58 


37l 


II26.67 


27i 


583.21 


32f 


835-97 


38 


II34.12 


27-1 


588.57 


32f 


842.39 


38i 


II41.59 


27i 


593-96 


32| 


848.83 


38i 


II49.09 


27I 


599-37 


33 


855.30 


38| 


II56.61 


27i 


604.81 


33i 


861.79 


38i 


1164.16 


271 


610.27 


33i 


868.31 


38f 


1171.73 


28 


6i5-75 


33f 


874.85 


3« 


H79-33 


28£ 


621.26 


33i 


881.41 


38f 


1186.95 


28i 


626.80 


33* 


888.00 


39 


1194.59 


28ff 


632.36 


33* 


894.62 


29i 


1202.26 


2S+ 


637.94 


33f 


901.26 


39i 


1209.96 


28f 


643.55 


34 


907.92 


39i 


1217.68 


28I 


649.18 


34i 


914.61 


39i 


1225.42 


28i 


654.84 


34i 


921.32 


39* 


1233.19 


29 


660.52 


34l 


928.06 


39i 


1240.98 


29i 


666.23 


34i 


934.82 


39* 


1248.80 


2 9 i 


671.96 


34f 


941.61 


40 


1256.64 


29I 


677.71 


34i 


948.42 


40i 


1264.51 


29^- 


683.49 


34f 


955-25 


40i 


1272.40 


29! 


689.30 


35 


962.11 


40f 


1280.31 


zgi 


695.13 


35i 


969 . 00 


4o£ 


1288.25 



1 5 6 



TN DIC A TOR PRACTICE. 
TABLE I — Continued. 



Diameter 


Area in square 


Diameter 


Area in square 


Diameter 


Area in square 


in inches. 


inches. 


in inches. 


inches. 


in inches. 


inches. 


4<>f 


1296.22 


46 


1661.91 


52f 


2185.42 


40} 


1304.21 


46£ 


1670.95 


53 


2206.18 


40J 


1312.22 


46i 


1680.02 


53i 


2227.05 


41 


1320.26 


46f 


1689. II 


53i 


2248.OI 


4ii 


1328.32 


46£ 


1698.23 


53* 


2269.07 


4ii 


1336.41 


46f 


1707.37 


54 


2290.22 


41* 


1344.52 


46f 


1716.54 


54i 


2311.48 


4i* 


1352.66 


46| 


1725.73 


54* 


2332.84 


4if 


1360.82 


47 


i # 734-95 


54* 


2354.29 


4if 


1369.OO 


47i 


1744.19 


55 


2375.83 


4i| 


1377 21 


47i 


1753-45 


55i 


2397.48 


42 


I385-45 


471 


1762.74 


55* 


2419.23 


42i 


I393.7O 


47i 


1772.06 


551 


2441.07 


42i 


I4OI.99 


474 


1781.40 


56 


2463.01 


421 


I4IO.3O 


474 


1790.76 


56i 


2485.05 


42i 


I418.63 


47f 


1800.15 


56* 


2507.19 


42f 


I426.99 


48 


1809.56 


56f 


2529.43 


42f 


1435-37 


4H 


1819.00 


57 


2551.76 


42| 


1443-77 


4H 


1828.46 


57i 


2574.20 


43 


1452.20 


m 


I837.95 


57* 


2596.73 


43i 


1460.66 


4H 


1847.46 


571 


2619.36 


43i 


1469.14 


48I 


1856. 99 


58 


2642.08 


431 


1477.64 


48f 


1866.55 


58i 


2664.91 


43i 


1486.17 


48J 


1876.14 


58* 


2687.84 


43f 


1494.73 


49 


1885.75 


58f 


2710.86 


43* 


1503.30 


49i 


1895.38 


59 


2733-97 


43| 


1511.91 


49i 


1905.04 


59* 


2757.20 


44 


1520.53 


* 49f 


1914.72 


59* 


2780.51 


44i 


1529.19 


49i 


1924.43 


59* 


2803.93 


44i 


1537.86 


494 


1934.16 


60 


2827.44 


441 


1546.56 


49f 


1943.91 


6oi 


2851.05 


44i 


1555.29 


49* 


1953.69 


6o£ 


2S74.76 


444 


1564.04 


50 


1963.50 


6o£ 


2S98.57 


44* 


1572.81 i 


5oi 


19S3.18 


61 


2922.47 


44j 


1581.61 


5oi 


2002 . 96 


6ii 


2946.48 


45 


1590.43 


50f 


2022.86 


6r* 


2970.58 


45j 


1599.28 


5i 


2042.82 


6if 


2994.78 


45i 


1608.16 


5ii 


2062 . 90 


62 


3019.08 


451 


1617.05 


SH 


2083.08 


621 


3043.47 


45* 


1625.97 


5if 


2103.35 


62| 


3067.97 


45f 


1634.92 


52 


2123.72 


62f 


3092.56 


45* 


1643.89 


52i 


2144 18 


63 


3117.25 


45| 


1652.89 


52^ 


2164.76 


63* 


3142.04 



TABLES. 
TABLE I. — Co7ttinued. 



157 



Diameter 


Area in square 


Diameter 


Area in square 


Diameter 


Area in square 


in inches. 


inches. 


in inches. 


inches. 


in inches. 

1 


inches. 


6 3 i 


3166.03 


74i 


4329.96 


85 


5674.5I 


63i 


3191.91 


74* 


4359-17 


85i 


5707.94 


64 


3217.OO 


74l 


4388.47 


85i 


5741-47 


64i 


3242.18 


75 


4417.87 


85f 


5775-IO 


64+ 


3267.46 


75i 


4447.38 


86 


5808.82 


64f 


3292.84 


75i 


4476.98 


86J 


5842.64 


65 


33I8.3I 


75* 


4506.67 


86J 


5876.56 


65i 


3343-86 ; 


76 


4536.47 


86f 


5910.58 


65i 


3369-56 


7 6i 


4566.36 


87 


5944.69 


651 


3395.33 


76i 


4596.36 


87i 


5978.91 


66 


3421.20 


76! 


4626.45 


87i 


6013.22 


6<± 


3447.17 


77 


4656.64 


87* 


6047.63 


60 , 


3473.24 


77i 


4686.92 


88 


6082.14 


66| 


3499.40 


77* - 


4717.31 


88i 


6116.74 


67 


3525.66 


771 


4747-79 


88i 


6151.45 


67i 


3552.02 


78 


4778.37 


88f 


6186.25 


67^ 


3578.48 


7Si 


4809.05 


89 


6221.15 


67i 


3605.04 


78* 


4839.83 


89i 


6256.15 


68 


3631.69 


78t 


4870.71 


89i 


6291.25 


68i 


3658.44 


79 


4901.68 


8gf 


6326.45 


68+ 


3685.29 


79* 


4932.75 


90 


6361.74 


68f 


3712.24 


79* 


4963.92 


90J 


6397.I3 


69 


3739-29 


79i 


4995 • 19 


9oi 


6432.62 


6 9 i 


3766.43 


80 


5026.56 


9 of 


6468.21 


69^- 


3793-68 


SoJ- 


5058.03 


9i 


6503.90 


6 9 f 


3821.02 


8o£ 


5089.59 


9ii 


6539.68 


70 


3848.46 


8of 


5121.25 


9*i 


6575.56 


7<4 


3876.OO 


81 


5I53.0I 


9If 


6611.55 


7o* 


3903.63 


8ii 


5184.87 


92 


6647.63 


7of 


3931-37 


8i| 


5216.82 


92! 


6683.80 


7i 


3959- 20 


8 if 


5248.88 


92i 


6720.08 


7ii 


3987.13 


82 


5281.03 


92f 


6756.45 


7i* 


4015.16 


82i 


5313.28 


93 


6792.92 


7if 


4043.29 


82i 


5345.63 


93i 


6829.49 


72 


4071.51 


82f 


5378.o8 


93i 


6866.16 


72i 


4099.84 


S3 


5410.62 


931 


6902.93 


72i 


4128.26 


83i 


5443.26 


94 


6939.79 


72f 


4156.78 


83* 


5476.oi 


94i 


6976.76 


73 


4185.40 


83f 


5508.84 


94i 


7013.82 


73i 


4214. 11 


84 


5541.78 


94i 


7050.98 


73i 


4242.93 


84i 


5574-82 


95 


7088.24 


73f 


4271.84 


84* 


5607.95 


95i 


7125.59 


74 


4300.85 


8 4 f 


5641.18 


95i 


7163.04 



i 5 8 



INDICATOR PRACTICE. 
TABLE I. — Continued. 



Diameter 


Area in square 


Diameter 


Area in square 


Diameter 


Area in square 


in inches. 


inches. 


in inches. 


inches. 


in inches. 


inches. 


951 


7200.60 


97i 


7427.97 


98f 


7658.88 


96 


7238.25 


97i 


7466.21 


99 


7697.71 


0i 


7275.99 


97i 


7504.55 


99* 


7736.63 


96^ 


73I3.84 


98 


7542.98 


99i 


7775-66 


961 


735L79 


Q8i 


7581.52 


99f 


7S14.78 


97 


7389.83 


98i 


7620.15 


100 


7S54.00 



The area of a circle larger than in the table may be 
found by squaring the diameter and multiplying the 
product by the decimal .7854; but it may generally be 
more easily found by the use of the table. Thus, to find 
the area of a circle 120 inches = 10 feet diameter, find 
in the table the area of a circle 10 inches diameter and 
multiply by 144, the number of square inches in a foot. 
The area of a 10-inch circle is 78.54 square inches, and 
of a 10-foot circle 78.54 square feet, or 78.54 X I44 z = 
11309.76 square inches. Again, the areas of circles 
vary as the squares of their diameters ; hence, to find 
the area of, say, a circle 150 inches diameter, find in 
the table the area of a 75-inch circle and multiply by 4 ; 
or find the area of a 50-inch circle and multiply by 9. 






TABLES, 



159 



TABLE II. 

Properties of Saturated Steam. 

{Abridged from Tables calculated by Charles T. Porter.) 



Absolute 
pressure in 


Temperature 
in de°"rees 


Heat-units per 
pound 


Heat-units 
per pound 


Weight in 
decimals of a 


Specific 


pounds per 


Fahrenheit. 


reckoning 


contained in 


pound per 


volume. 


square inch. 


from zero. 


the water. 


cubic foot. 




I 


102 


II45 


I02. 1 


.0030 


20620 


2 


I26.3 


II52.5 


126.4 


.0058 


IO720 


3 


141. 6 


II57.I 


141. 9 


.0085 


7326 


4 


153. 1 


I 160. 6 


153-4 


.0112 


5600 


5 


162.3 


1163.4 


162.7 


.OI37 


4535 


6 


170. 1 


1165.8 


170.6 


.0163 


3814 


7 


176.9 


1167.9 


177-4 


.O1S9 


3300 


8 


182.9 


1169.7 


183.5 


.0214 


2910 


9 


188.3 


1171.4 


188.9 


.0239 


2607 


10 


193.2 


1172.9 


193.9 


.0264 


2360 


11 


197.8 


H74-2 


193.5 


.0289 


2157 


12 


202 


II/5-5 


202.7 


.0313 


1988 


13 


205.9 


1176.7 


206.7 


.0337 


1846 


*4 


209.6 


1177.9 


210.4 


.0362 


1722 


14.7 


212 


1178.6 


212.9 


.O380 


1644 


15 


213. 1 


1178.9 


213.9 


.0387 


i6r2 


16 


216.3 


H79-9 


217.2 


.0413 


1514 


17 


219.4 


1180.9 


220.4 


.0437 


1427 


18 


222.4 


1181.8 


223.4 


.O462 


1351 


19 


225.2 


1182.6 


226.3 


.O487 


1282. 1 


20 


227.9 


1183.5 


229 


.05II 


1220.3 


21 


23O.5 


1184.2 


231.7 


.0536 


1164.4 


22 


233 


1185 


234.2 


.0561 


IH3-5 


23 


235-4 


1185.7 


236.7 


.0585 


1066.9 


24 


237.7 


1186.5 


239 


.o6lO 


1024. 1 


25 


240 


1187.1 


241.3 


.0634 


984.8 


26 


242.2 


1187.8 


243-5 


.0658 


948.4 


27 


244-3 


1188.5 


245.7 


.0683 


914.6 


28 


246.3 


1189 


247.7 


.0707 


883.2 


29 


248.3 


1189.7 


249.8 


.0731 


854 


30 


250.2 


1190.3 


251.7 


•0755 


826.8 


3i 


252.1 


1 190. 8 


253.6 


.0779 


801.2 


32 


254 


1191.4 


255-5 


.0803 


777-2 


33 


255.7 


1191.9 


257-3 


.0827 


754-7 



i6o 



INDICATOR PRACTICE. 



TABLE II.—- Continued. 



Absolute 


Temperature 
in degrees, 
Fahrenheit. 


Heat-units per 


Heat-units 


Weight in 




pressure in 


pound, 


per pound 


decimals of a 


Specific 


pounds per 


reckoning 


contained in 


pound per 


volume. 


square inch. 


from zero. 


the water. 


cubic foot. 




34 


257.5 


II92.5 


259-1 


.0851 


733-5 


35 


259.2 


1193 


260.8 


.0875 


713.4 


36 


260.9 


II93.5 


262.5 


.0899 


694.5 


37 


262.5 


1 194 


264.2 


.0922 


676.6 


38 


264 


II94.5 


265.8 


.0946 


659.7 


39 


265.6 


1195 


267.4 


.0970 


643.6 


40 


267.I 


II95.4 


268.9 


.0994 


628.2 


4i 


268.6 


II95.9 


270.5 


.1017 


613.4 


42 


270.I 


II96.3 


272 


.IO41 


599-3 


43 


271.5 


II96.7 


273-4 


.1064 


586.1 


44 


272.9 


II97.2 


274.9 


.1088 


573.7 


45 


274.3 


II97.6 


276.3 


.1111 


561.8 


46 


275-7 


II98 


277.7 


.1134 


550.4 


47 


277 


II98.4 


279 


.1158 


539-5 


48 


278.3 


II98.8 


280.4 


.Il8l 


529 


49 


279.6 


II99.2 


281.7 


.1204 


518.6 


5o 


280.9 


H99.6 


283 


.1227 


508.5 


5i 


282.I 


I200 


284.2 


.1251 


499.1 


52 


283.3 


1200.4 


285.5 


.1274 


490.1 


53 


284.5 


I200.7 


286.7 


.1297 


481.4 


54 


285.7 


I20I.I 


288 


.1320 


472.9 


55 


286.9 


I20I.4 


289.2 


•1343 


464.7 


56 


288.1 


1201.8 


290.3 


.1366 


457 


57 


289.I 


1202. I 


29I.5 


.1388 


449.6 


58 


290.3 


I202-5 


292.7 


.1411 


442.4 


59 


291.4 


I202.8 


293.8 


.1434 


435.3 


60 


292.5 


I203.2 


294.9 


.1457 


428.5 


61 


293.6 


I203.5 


296 


.1479 


422 


62 


294.7 


I203.8 


297.I 


.1502 


415.6 


63 


295.7 


I204. I 


298.2 


.1525 


409.4 


64 


296.8 


1204.5 


299.2 


.1547 


403.5 


65 


297.8 


1204.8 


300.3 


.1570 


397-7 


66 


298.8 


I205. I 


30I.3 


.1592 


392.1 


67 


299.8 


I205.4 


302.4 


.1615 


386.6 


68 


300.8 


1205.7 


303.4 


.1637 


381.3 


69 


301.8 


I206 


304.4 


.1660 


376.1 


70 


302.7 


I206.3 


305.4 


.1682 


371.2 


7i 


303.7 


I206.6 


306.4 


.1704 


366.4 


72 


304-6 


I206.9 


307.3 


.1726 


361.7 


73 


305.6 


I207. I 


308.3 


.1748 


357-1 


74 


306.5 


I207.4 


309.3 


.1770 


352 6 



TABLES, 



161 



TABLE II.— Continued. 



Absolute 


Temperature 
in degrees, 

Fahrenheit. 


Heat-units per 


Heat-units 


Weight in 




pressure in 


pound, 


per pound 


decimals of a 


Specific 


pounds per 


reckoning 


contained in 


pound per 


volume. 


square inch. 




f 10m zero. 


the water. 


cubic foot. 




75 


307.4 


1207.7 


3IO.2 


.1792 


348.3 


76 


308.3 


I208 


311. 1 


.1814 


344-1 


77 


309.2 


I208.2 


312 


.1836 


340 


78 


3IO. I 


1208.5 


313 


.1858 


336 


79 


3IO.9 


1208.8 


313.8 


.1880 


332.1 


80 


311. 8 


1209 


3I4.7 


.I90I 


328.3 


81 


312.7 


1209.3 


315-6 


.1923 


324.6 


82 


313-5 


1209.6 


316.5 


•1945 


320.9 


83 


314-4 


1209.8 


3I7-3 


.1967 


317.3 


84 


315-2 


I2IO 


318.2 


.1989 


313-9 


85 


316 


I2I0.3 


319 


.2010 


310.5 


86 


316.8 


1210.6 


3i9'9 


.2032 


307.2 


87 


317.6 


1210.8 


320.7 


.2053 


304 


88 


3i8.5 


I2II 


321.5 


♦2075 


300.8 


89 


319-3 


I2II.3 


322.4 


.2097 


297.7 


90 


320 


I2II.6 


323.2 


.2118 


294.7 


9i 


320.8 


I2II.8 


324 


.2139 


291.8 


92 


321.6 


1212 


324.8 


.2l6l 


288.9 


93 


322.4 


I2I2.3 


325.6 


-2183 


286.1 


94 


323.1 


I2I2.5 


326.4 


.2204 


283.3 


95 


323.9 


I2I2.7 


327.1 


.2225 


280.6 


96 


324.6 


1213 


327-9 


.2245 


278 


97 


325.4 


I2I3.2 


328.7 


.2267 


275-4 


98 


326.1 


I213.4 


329.4 


.2288 


272.8 


99 


326.8 


I2I3.6 


330.2 


.2309 


270.3 


100 


327.6 


I2I3.8 


33i 


.2330 


267.9 


IOI 


328.3 


1214 


331-7 


.2351 


265.5 


102 


329 


I214.3 


332.4 


.2372 


263.2 


103 


329-7 


I214.5 


333-1 


.2392 


260.9 


104 


330.4 


I214.7 


333-9 


.2413 


258.7 


105 


33i- 1 


I214.9 


334-6 


.2434 


256.5 


106 


331.8 


I2I5.I 


335-3 


•2455 


254-3 


107 


332.5 


I2I5.3 


336 


•2475 


252.2 


108 


333-2 


I2I5.6 


336.7 


.2496 


250.1 


109 


333-9 


I2I5.8 


337.4 


.2517 


248 


no 


334-5 


I2l6 


338.1 


.2538 


246 


III 


335-2 


I2I6.2 


338.8 


.2558 


244 


112 


335-9 


I2I6.4 


339-5 


.2579 


242 


113 


330.5 


I2I6.6 


340.2 


.2599 


240.1 


114 


337-2 


I2I6.8 


340.8 


.2620 


238.2 


115 


337.8 


1217 


341.5 


.2640 


236.3 


Il6 


338.5 


I2I7.2 


342.2 


.2661 


234-5 



1 62 



INDICATOR PRACTICE. 
TABLE II.— Continued. 



Absolute 


Temperature 
in degrees, 
Fahrenheit. 


Heat-units per 


Heat units 


Weight in 




pressure in 


pound, 


per pound 


decimals of a 


Specific 


pounds per 


reckoning 


contained in 


pound per 


volume. 


square inch. 




from zero. 


the water. 


cubic foot. 




"7 


339-1 


1217.4 


342.8 


.2682 


232.7 


118 


339-7 


1217.6 


343.5 


.2702 


231 


II 9 


340-4 


I217.8 


344-2 


.2722 


229.3 


120 


34i 


I217.9 


344-8 


.2743 


227.6 


121 


341.6 


I2I8.I 


345-4 


.2763 


226 


122 


342.2 


I218.3 


346.1 


.2783 


224.4 


123 


342.9 


I2I8.5 


346.7 


.2803 


222.8 


124 


343-5 


1218.7 


347-3 


.2823 


221.2 


125 


344-1 


1218.9 


348 


.2843 


219.7 


126 


344-7 


1219.I 


348.6 


.2862 


218.2 


127 


345-3 


1219.3 


349.2 


.2882 


2l6.7 


128 


345-9 


1219.4 


349-8 


. 2902 


215.2 


129 


346.5 


1219.6 


350.4 


.2922 


213-7 


I30 


347-1 


1219.8 


351- 1 


.2942 


212.3 


131 


347.6 


I220 


351-7 


.2962 


2IO.9 


132 


348.2 


I220.2 


352.3 


.2982 


209.5 


133 


348.8 


1220.4 


352.9 


.3001 


208.I 


134 


349-4 


I220.5 


353.5 


.3021 


206.7 


135 


350 


I220-7 


354-1 


.3040 


205.4 


I36 


350.5 


I220-9 


354-6 


.3060 


204.I 


137 


351-1 


1221 


355-2 


.3080 


202.8 


I38 


351.7 


1221.2 


355-8 


.3099 


201.5 


139 


352.2 


I22I-4 


356.4 


•3119 


200.2 


I40 


352.8 


I22I.5 


357 


.3139 


199 


141 


353-3 


I22I.7 


357-5 


.3159 


I97.8 


142 


353-9 


I22I.9 


358.1 


.3179 


I96.6 


143 


354-4 


1222 


358.7 


.3199 


195-4 


144 


355 


1222.2 


359-2 


.3219 


194.2 


145 


355-5 


1222.4 


359-8 


.3239 


193 


I46 


356 


1222.5 


360.4 


.3259 


191. 9 


147 


356.6 


1222.7 


360.9 


.3279 


I90.8 


I48 


357-1 


1222.9 


361.5 


.3299 


189.7 


149 


357-6 


1223 


362 


.3320 


188.6 


ISO 


358.1 


1223.2 


362.6 


.3340 


187.5 


151 


358.7 


1223.3 


363-1 


.3358 


186.4 


152 


359-2 


1223.5 


363.6 


.3376 


185.3 


153 


359-7 


1223.7 


364.2 


•3394 


184.3 


154 


360.2 


I223.9 


364.7 


.3412 


183.3 


155 


360.7 


1224 


365.2 


.3430 


182.3 


156 


361.2 


1224. I 


365.8 


.3448 


181. 3 


157 


361.8 


I224.3 


366.3 


.3467 


180.3 


I58 


362.3 


I224.4 


366.8 


.3485 


179-3 



TABLES. 
TABLE II.— Continued. 



163 



Absolute 
pressure in 


Temperature 
in degrees, 
Fahrenheit. 


Heat-units per 
pound, 


Heat-units Weight in 
per pound decimals of a 


Specific 


pounds per 


reckoning 


contained in pound per 


volume. 


square inch. 




from zero. 


the water. cu 


bic foot. 




159 


362.8 


1224.6 


367.3 


.3503 


178.3 


160 


363.3 


1224.8 


367.9 


.3521 


177-3 


l6l 


363.8 


1224.9 


368.4 


•3540 


176.4 


162 


364.3 


1225 


36S.9 


.3558 


175.5 


163 


364.8 


1225.2 


369.4 


•3577 


174.6 


164 


365.2 


I225.3 


369.9 


.3596 


173.7 


165 


365.7 


1225.5 


370.4 


.3615 


172.8 


166 


366.2 


1225.6 


370.9 


•3634 


171. 9 


167 


366.7 


I225.8 


371 4 


.3652 


171 


168 


367.2 


1225.9 


371.9 


.3671 


170. 1 


169 


367.7 


1226. I 


372.4 


.3690 


169.2 


170 


363.2 


1226.2 


372.9 


.3709 


168.4 


171 


363.6 


1226.4 


373-4 


.3727 


167.6 


172 


369.I 


1226.5 


373-9 


•3745 


166.8 


173 


369.6 


1226.7 


374-4 


3763 


166 


174 


370 


1226.8 


374-9 


3781 


165.2 


175 


370.5 


1226.9 


375-4 


3799 


164.4 


176 


371 


1227. I 


375-9 


3817 


163.6 


177 


371.4 


1227.2 


376.3 


3835 


162.8 


I 7 S 


371.9 


1227.4 


376.8 


3853 


162 


179 


372.4 


I227.5 


377-3 


3871 


161. 2 


180 


372.8 


T227.7 


377-8 


3889 


160.4 


l8l 


373-3 


1227.8 


378.3 


3908 


159-7 


182 


373.7 


1227.9 


378.7 


3926 


159 


183 


374-2 


1228. I 


379-2 


3944 


158.3 


184 


374-6 


1223.2 


379-7 


3962 


157.6 


185 


375-1 


1228.3 


380.1 


398i 


156.9 


186 


375-5 


1228.5 


380.6 


3999 


156.2 


187 


376 


1228.6 


381. 1 


4017 


155-5 


188 


376.4 


1228.7 


381.5 


4036 


154-8 


189 


376.9 


I228.9 


382 


4054 


154-r 


190 


377-3 


1229 


382.4 


4072 


153.4 


191 


377-7 


I229. I 


382.9 


4090 


152.7 


192 


378.2 


I229.3 


383.3 


4108 


152 


193 


378.6 


I229.4 


383.8 


4125 


151. 3 


194 


379 


I229.5 


384-2 


4143 


150.7 


195 


379-5 


I229.7 


384.7 


4160 


150. 1 


196 


380 


1229.8 


385.1 


4178 


149.5 


197 


380.3 


I229.9 


385-6 


4196 


148.9 


198 


3S0.7 


I23O. I 


386 


4214 


148. 3 


199 


381. 1 


I230.2 


386.5 


4232 


147.7 


200 


381.6 


I23O.3 


386.9 


4250 


147. 1 



164 INDICATOR PRACTICE. . 

In Table II. the column of temperature is the tem- 
perature, or sensible heat of steam, and the water with 
which it is in contact. 

Under Specific Volume is given the volume of steam 
at different pressures as compared with water. Thus, 
at 80 pounds absolute pressure steam occupies space 
328.3 greater than water. 

The heat-units contained in water at temperatures 
less than 102 , the lowest given in the table, may, 
without material error, be taken as the same as the 
temperature of the water. 

The latent heat of steam is not given in the table, but 
may be readily found by subtracting the heat -units 
contained in the water from those contained in the 
steam. As, for example, steam at 90 pounds absolute 
pressure contains 121 1.6, and water of a corresponding 
temperature 323.2 heat-units. Subtract the last-named 
number from the first, and the remainder is 888.4, 
which is the latent heat of steam at that pressure. 

ECONOMY OF HEATING FEED-WATER. 

Suppose the feed-water is at a temperature of 6o°, 
and boiler- pressure 70 pounds, what would be the 
gain due to heating the water by exhaust-steam to a 
temperature of 202 ? Seventy pounds pressure by 
gauge is (about) 85 pounds absolute. From the table 
the total heat of 1 pound of steam of that pressure is 
found to be 12 10.3 heat-units. The water contains 60 
units, leaving to be imparted 12 10.3 — 60 = 1 1 50.3. 
In the heater 202.7 — 60 = 142.7 heat -units are im- 
parted to the pound of water, a saving by the use of 
the heater of 142.7 -=- 11 50.3 = 12 -f- per cent. 



TABLES. 165 

THE EVAPORATIVE DUTY OF BOILERS. 

The evaporative duty of boilers is usually given from 
and at 21 2°, in which the heat required to vaporize the 
water from that temperature, and under the pressure of 
the atmosphere, is accounted for. By the use of Table 
II. the evaporation from any temperature of feed-water, 
and at any pressure up to 200 pounds per square inch, 
can be reduced to standard evaporation. Suppose a 
boiler is evaporating 8 pounds of water of a tempera- 
ture of 50 into steam of an absolute pressure of 100 
pounds, what is the equivalent evaporation from and 
at 212° ? The heat-units per pound of steam of 100 
pounds pressure are 1 213.8, which, less 50 contained 
in the water, leaves 1 163.8 to be imparted. The heat 
units in steam of 21 2° temperature is, by the table, 
1 1 78.6, and of the water 212.9. To evaporate water 
from and at 212° requires then 1 178.6 — 212.9= 965.7 
heat-units per pound. Multiplying the actual evapora- 
tion, 8 pounds, by 1 163.8, and dividing by 965.7, we 
have 9.64 pounds as the equivalent evaporation from 
and at 212 . 



i66 



INDICATOR PRACTICE. 



TABLE III. 

HYPERBOLIC LOGARITHMS -f- I. 



Num- 


Hyperbolic 


Num- 


Hyperbolic 


Num- 


Hyperbolic 


Num- 


Hyp'bolic 


ber. 


Log. + 1. 


ber. 


Log. -f 1. 


ber. 


Log. 4- 1. 


ber. 


Log. + i. 


I.I 


I.O95 


4.4 


2.482 


7.7 


3.041 


20 


3.996 


1.2 


1. 182 


4 


5 


2.504 


7 


8 


3.054 


21 


4-045 


1-3 


I.262 


4 


6 


2.526 


7 


9 


3.067 


22 


4.09I 


1-4 


1-336 


4 


7 


2.548 


8 




3.079 


23 


4-135 


15 


I.405 


4 


8 


2.569 


8 


1 


3-092 


24 


4.178 


1.6 


I.470 


4 


9 


2.589 


8 


2 


3.I04 


25 


4.219 


1.7 


I. 531 


5 




2.609 


8 


3 


3« HO 


26 


4.258 


1.8 


1.588 


5 


1 


2.629 


8 


4 


3-128 


27 


4.296 


1.9 


I.642 


5 


2 


2.649 


8 


5 


3.140 


28 


4.332 


2 


I.693 


5 


3 


2.668 


8 


6 


3-I5I 


29 


4.367 


2.1 


I.742 


5 


4 


2.686 


8 


7 


3.163 


30 


4.401 


2.2 


I.788 


5 


5 


2.705 


8 


8 


3.185 


31 


4-434 


2.3 


I.833 


5 


6 


2.723 


8 





3.186 


32 


4.466 


2.4 


1.875 


5 


7 


2.740 


9 




3.197 


33 


4-497 


2.5 


1. 916 


5 


8 


2.758 


9 


1 


3.208 


34 


4.526 


2.6 


1.955 


5 


9 


2.775 


9 


2 


3.219 


35 


4-555 


2.7 


1-993 


6 




2.792 


9 


3 


3.230 


36 


4.584 


2.8 


2.030 


6 


1 


2.808 


9 


4 


3.241 


37 


4. 611 


2.9 


2.065 


6 


2 


2.825 


9 


5 


3251 


38 


4.638 


3 


2.099 


6 


3 


2.841 


9 


6 


3-261 


39 


4.664 


3-i 


2. 131 


6 


4 


2.856 


9 


7 


3-272 


40 


4.689 


3-2 


2.163 


6 


5 


2.872 


9 


8 


3-283 


45 


4.807 


3-3 


2.I96 


6 


6 


2.887 


9 


9 


3.292 


50 


4.912 


3.4 


2.224 


6 


7 


2.902 


10 


3.303 


55 


5.007 


3-5 


2.253 


6 


8 


2.917 


11 


3.39 6 


60 


5.094 


3.6 


2.281 


6 


9 


2.931 


12 


3.485 


65 


5.174 


3-7 


2.308 


7 




2.946 


13 


3-565 


7o 


5.248 


3-8 


2.330 


7 


.1 


2.960 


14 


3.639 


75 


5.317 


39 


2.361 


7 


2 


2.974 


15 


3.7o8 


80 


5.382 


4 


2.386 


7 


3 


2.988 


16 


3-773 


85 


5-443 


4-1 


2. 4II 


7 


4 


3.001 


17 


3.833 


90 


5.5oo 


4.2 


2-435 


7 


5 


3.oi5 


18 


3.890 


95 


5-554 


4-3 


2-459 


7.6 


3.028 


!9 


3-944 


100 


5.605 






TABLES. 



167 



TABLE IV. 

COMMON FRACTIONS WITH THEIR DECIMAL EQUIVALENTS. 



Common 


Decimal 


Common 


Decimal 


Common 


Decimal 


fraction. 


equivalent. 


fraction. e 


:juivalent. 


fraction. 


equivalent. 


1 

6T 


.0156 + 


11 

32 


3437 + 


43 

6¥ 


.6718 + 


A 


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1 68 INDICATOR PRACTICE. 



CHAPTER XIX. 
TESTING ENGINES AND BOILERS. 

ABSOLUTE EXACTNESS NOT POSSIBLE. 

EXPERT tests of engines and boilers, however care- 
fully and skilfully conducted, cannot be relied upon as 
being absolutely exact. There are chances for slight 
mistakes and elements of doubt which, while they may 
not very materially affect the results, will in a slight 
degree render them uncertain. The best that can be 
said cf any tests of engines and boilers is that they are 
fairly accurate if the necessary care is taken in making 
them. But to be of any value every possible precaution 
should be taken to avoid and modify errors. 

DIFFERENT WAYS OF MAKING TESTS. 

There are several ways of testing a steam-engine. 
One of these — in which the heat in the exhaust-steam, 
that converted into work, radiated, etc., is accounted 
for — is too complicated for ordinary purposes, and will 
not be further referred to. 

In one of the plans in common use account is taken 
of the coal burned, the result appearing as coal per 
horse-power per hour. By this plan the engine and 
boiler are considered together; hence it is a test of the 
steam-plant rather than of the engine. In some in- 
stances this may be exactly what is required ; in others 






TESTING ENGINES AND BOILERS. 1 69 

it is desirable to determine the economical efficiency 
of the engine without reference to the boiler furnish- 
ing the steam. Then it is customary to measure the 
water used, the result appearing as water per horse- 
power per hour. There is, generally speaking, less- 
chance for error in calculating the economy of the 
plant as a whole than in finding that of either the en- 
gine or boiler separately. 

DETERMINING THE COAL USED PER HORSE-POWER PER 

HOUR. 

When this is what is required the work done by the 
engine in a given time is measured, and the coal 
burned in doing it weighed. A run of not less than 
IO hours should be made when at all practicable ; in 
fact it is better to extend the run to 20 or 24 hours. 
The greatest chances for error are at the beginning 
and conclusion of the test, and the greater the interval 
the less the final result will be affected by errors oc- 
curring at these times. 

MEASURING THE INDICATED HORSE-POWER. 

For this purpose diagrams from both ends of the 
cylinder at intervals of 15 minutes will ordinarily be 
sufficient. At the conclusion of the run these are to 
be calculated, and the average mean effective pressure 
of all used in determining the horse-power. This in 
most cases will give the mean horse-power practically 
correct ; there may be special cases, when the power is 
extremely variable, where diagrams should be taken 
oftener than at intervals of 15 minutes. The judg- 
ment of the engineer must be used to get at a fair 



170 INDICATOR PRACTICE. 

average of the work done ; nothing in the way of sug- 
gestion can take the place of this. 

Since measuring a large number of diagrams is some- 
what tedious, it is always advisable to take precautions 
to shorten this operation. If a planimeter is used for 
measuring the area of diagrams it is worth while to be 
at some pains to adjust the drum-motion to get them 
even inches, or inches and half-inch, long. The pro- 
cess of computing the mean effective pressure by the 
use of the planimeter consists in finding the mean 
height of the diagram by dividing the area (taken from 
the reading) by the length, then multiplying this height 
by the scale of the spring. Sometimes the fractional 
part of the length is very awkward, and makes the 
process a long one. By a little attention the length of 
the diagram may be made such that the division 
will be much simplified, or that by cancellation with 
the number representing the scale of the spring no 
division will be necessary. 

DETERMINING THE COAL BURNED. 

This is by no means easy of accomplishment. Sev- 
eral plans, with various modifications, are employed, 
each of which has its advocates. One is to raise steam 
to working pressure, then draw the fire, and build a 
new one, weighing and charging up all wood and coal 
used to the termination of the test. To reduce the 
wood to its equivalent in coal, multiply the pounds of 
wood used by 0.4. Thus, if 50 pounds of wood are 
used in starting the new fire the equivalent in coal will 
be 50 X 0.4 = 20 pounds. 

At starting the fire, the water-level and steam-pres- 



TESTING ENGINES AND BOILERS. I? I 

sure should be accurately noted, and these should be 
exactly the same at stopping the engine; they should 
also, as far as practicable, be kept constant during the 
entire run. The time of starting and stopping the 
engine should be carefully noted ; the interval is the 
duration of the test. 

Immediately at the conclusion of the test the fire 
should be drawn and quenched, and the unconsumed 
coal picked out, weighed, and deducted from that 
charged up as being used. If it is desired to find the 
combustible used, everything that comes from the fire 
during and at the conclusion of the test should be 
weighed and deducted.^ 

The coal (and the equivalent in coal for the wood) 
supplied to the furnace, including that used in starting 
the fire, less the unconsumed coal weighed back, is the 
amount to be charged to the test. This divided by 
the average horse-power, and again by the duration in 
hours of the test, is the coal burned per horse-power 
per hour. 

Suppose for a run of 10 hours the average horse- 
power is 200 and the coal burned 4000 pounds; 4000 
divided by 200, and that again by 10, gives 2 pounds 
of coal per indicated horse-power per hour. 

An objection to this test is that there will inevitably 
be some loss in hauling the fire and rebuilding, by cold 
air coming in contact with the heating surfaces and the 
brick-work. There is also likelihood of a small loss in 
picking out the unconsumed fuel. 

After building a new fire it must get going suffi- 
ciently to keep up steam before the engine is started ; 
for this reason I have always found it advisable that 



I7 2 • INDICATOR PRACTICE. 

the steam be a little lower than the ordinary running 
pressure when the new fire is started. If the running 
pressure is 80 pounds, let it be 70 pounds when the 
fire is started, then start the engine when the pressure 
gets to 80 pounds; by this time the fire should be in 
condition to keep up steam. The stop should be mude 
at the conclusion of the test with the pressure at jb 
pounds. 

ANOTHER PLAN OF DETERMINING THE COAL. BURNED. 

Another plan is, before beginning the test, to clean 
the fire, and in the operation of cleaning — shoving 
back and distributing over the grate again — to estimate 
very carefully the quantity of clean coal on the grate, 
or at least to make such observations as will enable a 
comparison to be made with the fire similarly cleaned 
and treated at the conclusion. In this way the test 
can be begun and concluded without stopping the en- 
gine, unless it is necessary to do so to find the water- 
level, as in the instance of a boiler that raises the water 
considerably. 

There is the objection to this test, that some error 
is certain in estimating the coal on the grate. If the 
fire is low when cleaned, and the test is of not less 
than 10 hours' duration, the error should not be serious. 
Of course all conditions should be the same, as near as 
maybe, at starting and stopping; this is a requisite in 
any test of engine or boiler. Dependence should never 
be placed upon calculations by figures to equalize con- 
ditions, as, for instance, between observations at the 
beginning and termination of a test, when it is possible 
to make these conditions practically uniform. 



TESTING ENGINES AND BOILERS. 1 73 



WATER PER HORSE-POWER. 

In the water-test of a steam-engine the water sup- 
plied to the boiler during the test is weighed, and the 
total amount used divided by the average horse-power 
developed and by the duration, in hours, of the test. 
The result is water per indicated horse-power per hour. 
Thus, if, as before, the horse-power is 200, the duration 
of the test 10 hours, and the water used 40,000 pounds, 
then 40,000 divided by 200 and by 10 gives 20 pounds 
of water per horse-power. 

A test of this kind can be begun at any time by 
noting the steam-pressure and water-level, and there- 
after weighing the water supplied to the boiler. Some 
sort of tanks will have to be provided ; generally two 
barrels will answer. The arrangement should be such 
as to feed from one while the other is being filled. 

The chief objection to a water-test is the possibility 
of considerable water being carried from the boiler to 
the engine with the steam. This water will be charged 
to the engine, when its presence is harmful rather than 
helpful. Plans for determining the amount of water 
present in the steam are in use, but so far there is no 
dependence to be placed upon them, as shown by the 
most contradictory results obtained. Until those who 
have given much attention and thought to testing the 
quality of steam are able to do satisfactory work it will 
be useless for others to attempt it, unless indeed they 
can devise a plan superior to any at present practised. 
With well-constructed boilers the water carried over 
with the steam is not a serious quantity. With over- 
worked boilers of bad construction it may be a con- 



174 INDICATOR PRACTICE. 

siderable percentage — say, 10 per cent — of all the 
water suoplied. 

PUMPING-ENGINE DUTY AND TESTS. 

The economy of a pumping-engine is expressed by 
the use of the word " duty." This is the number of 
foot-pounds of work done by the consumption of ioo 
pounds of coal. Thus the duty of a pumping-engine 
that will do the equivalent of lifting 100,000,000 pounds 
one foot high for every 100 pounds of coal consumed 
is said to be 100,000,000. This has no reference to the 
capacity of the engine: that may be large or small. 
So far as the engine is concerned, this takes account of 
the effective and not the indicated power. It is usually 
calculated from the pressure against which the pump- 
piston works plus the equivalent pressure of lifting the 
water from the well. The resistance which the pump- 
piston must overcome is commonly determined by a 
pressure-gauge on the rising main ; to the pressure in- 
dicated by this gauge is added the pressure due to its 
height above the water in the well, measured when the 
pump is working. This is found by multiplying the 
height in feet by 0.433, the result appearing in pounds 
pressure per square inch. The sum of these pressures 
will be the resistance against which the pump-piston 
works. 

If this resistance is multiplied by the area of the pis- 
ton in inches, the length in feet of a double stroke 
(revolution), the number of double strokes (revolu- 
tions) in a given time and by 100, and divided by the 
pounds of coal burned during that time, the quotient 
will be duty. 






TESTING ENGINES AND BOILERS. 175 

For example, let the area of pump-piston be ioo 
inches, double stroke four feet, number of double 
strokes 9600, coal burned 800 pounds, the gauge on 
main show a pressure of 50 pounds, and the height of 
this gauge above water in well be 23.1 feet. 23.1 X 
0.433 = IO > which, added to 50 = 60 pounds, the resist- 
ance to motion of pump-piston. The duty will then be 

60 X 100 X 4 X 9600 X 100 



800 



= 28,800,000. 



It will be understood that the last multiplier, 100, is 
used because the divisor is the number of pounds of 
coal burned instead of the number of hundred pounds. 

Tests of pumping-engines may be begun either by 
starting new fires or estimating the amount of coal on 
the grate at the beginning and termination of the test. 
The water-pressure may vary considerably during the 
test, as when pumping direct into city mains, or since 
the dynamic head is the static head plus the friction 
when pumping into reservoirs, it will then vary with 
the speed of the pump ; hence it is necessary to take 
the reading of the water-gauge at frequent intervals, 
say, each quarter hour, and average all the readings. 

It is evident that the resistance against which the 
pump-piston moves might be calculated directly from 
diagrams from the pump-cylinder ; but this is not cus- 
tomary. The indicator should be applied to the pump- 
cylinder and diagrams taken during the test to deter- 
mine if the pump is working properly. If this is not 
done, it is possible to account for more work than is 
actually accomplished. Diagrams should also be taken 
from the steam-cylinder, and comparisons made with 



176 INDICATOR PRACTICE. 

the power developed there and the work credited to 
the pump. I have known instances in which the pump 
was given credit for more work than was done in the 
steam-cylinder. Of course the reverse of this should 
be true to the extent of the friction of the engine. 

Water-gauges, from the constant hammering they 
receive from the water, are subject to derangement, 
and sometimes, when the exact height to which the 
water is elevated is known, are not depended upon. 
In one test in which the writer was engaged the fol- 
lowing plan for determining the dynamic head was 
pursued : The total height to which the water was 
raised was known to be 231.283 feet. This had been 
determined both by surveys and by testing the static 
head by a proved gauge. To determine how much to 
add for friction, the readings of the gauge were taken 
with engine at work and at rest, and the difference 
found to be 9.607 feet — one foot was added for 
friction below gauge. These added to 231.283 gave 
the dynamic head as 241.89 feet — in pounds, 241.89 X 
0.433 = 104.738. It was believed that, although the 
gauge was not quite correct in total readings, it would 
not vary materially in less than 10 feet, equal to about 
4 pounds. This view was further strengthened by the 
fact that the friction allowance agreed with previous 
estimates of the hydraulic engineers, so 104.738 pounds 
per square inch was taken as the resistance against 
which the pump-piston worked. 

The custom has usually been in testing a pumping- 
engine to consider the plant — engine and boilers — as 
a whole. In fact from the understanding of the word 
duty it must be so considered. Sometimes, however, 
the duty guaranteed is on the assumption that the 



TESTING ENGINES AND BOILERS. 1/7 

boilers will evaporate a specified amount of water per 
pound of coal; if they fail to do this, an allowance 
covering the deficiency is made in favor of the engine. 
This is generally to cover the possible use of a poor 
quality of fuel. 

BOILER-TESTS. 

In boiler-tests the object is to find the quantity of 
water evaporated per pound of coal, and the quantity 
the boiler is capable of evaporating. By one of the 
methods previously explained the coal burned in a 
given time is determined, and also the water evaporated. 
The latter is a measure of the capacity of the boiler, 
and divided by the former shows the economy. The 
difficulties previously mentioned — water carried over 
with the steam, and in accurately determining the coal 
burned — will of course be encountered. 

In the preceding chapter the fact was alluded to 
that for uniformity it was customary to state the 
economy of a boiler in equivalent evaporation from 
and at 21 2°, and the process of making the reduction 
was explained. By the use of the following table, 
prepared for the American Machinist by a correspond- 
ent whose name I regret not being able to give, the 
process is very much shortened. The basis for this 
table are the steam-tables of Charles T. Porter. To 
use the table, multiply the observed evaporation by the 
factor under the pressure at which it took place, and 
against the temperature of feed. Thus, suppose the 
evaporation is 8^ pounds of water per pound of coal, 
the gauge-pressure being 80 pounds, and the tempera- 
ture of feed 130 . Under 80 and against 130 find the 
factor 1.121. Multiply 8J by this, and the product, 
9.52, is the equivalent evaporation from and at 21 2°. 



i/8 



INDICATOR PRACTICE. 



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TESTING ENGINES AND BOILERS. 1 79 



WHAT SHOULD BE NOTED. 



As these tests are supposed to be made by working 
engineers and mechanics for purposes purely practical, 
the record will not usually be as complete as if made 
by experts for purposes partly scientific. In testing 
an engine it is necessary that the steam-pressure be 
accurately noted at intervals sufficiently short to in- 
sure a correct average. One of the objects of a steam- 
engine test is to determine the economy under a given 
steam-pressure ; hence the importance of knowing ex- 
actly what that pressure is. If a condensing-engine, 
the vacuum by gauge should be similarly recorded, and 
other particulars given in Chapter V. When the boiler 
in any way enters into the test, temperatures in boiler- 
room and outside, and readings from a barometer 
when practicable, should be taken. If possible, the 
temperature of the escaping gases should be observed, 
and the temperature of the feed-water always ; in fact, 
any conditions that remotely affect the result should, 
when possible, be recorded. Particularly dimensions 
and location of grate, dimensions of chimney, size, 
length, and number of tubes, and other parts, should be 
noted. Things that seem of no importance at the 
time may have value at some future consideration of 
the record. Measures and weights should be accurate, 
and gauges and other instruments known to be correct. 
The habit of being exact and of extending the ob- 
servations made should be cultivated. 

By practice and observation an engineer in charge 
of a steam-plant, or a machinist who sets up engines 
and boilers, may make tests that will assist in deter- 



180 INDICATOR PRACTICE. 

mining the most economical plan of operating, and 
with but little trouble or preparation. Such tests 
frequently made by engineers are valuable, and owners 
of steam-engines and boilers should in every way en- 
courage them, as tending to greater economy in the 
use of fuel. 



INDEX. 



Absolute information from diagrams, 

26. 
Absolute pressure, 7. 
Adjusting valves, 13, 30. 
Admission, late, 103. 
Admission-line, 28. 
Admission-line, an impossible, 101. 
Air required for combustion, 39. - 
Areas of ciicles, table of, 153. 
Areas of large circles, finding, 158. 
Atmospheric line, 28. 
Atmospheric line, tracing, 24. 
Atmospheric pressure, 28. 

Back-pressure, 7, 35. 
Back-pressure, cause of excessive, 36. 
Back-pressure in condensing and non- 
condensing engines, 77. 
Back-pressure, loss from, 131. 
Back-pressure, note on, 8. 
Back-pressure, reduction for, 43. 
Back-pressure, total, 7. 
Blanks, example of printed, 25. 
Boiler-duty, 39. 

Boiler, evaporative duty of, 164. 
Boiler-pressure, 7. 
Boilers, testing, 168. 

Cast-iron, weight of, 149. 
Channelling the head or counter-bore, 

10. 
Clearance, 8, 57. 
Clearance, estimating, 92. 
Clearance-line, locating, 62. 
Clearance, per cent of, 64. 
Clearance, Professor Sweet's plan for 

measuring, 62. 



Clearance, the exact effect of, known 
only by trial, 128. 

Coal burned, determining, 170, 172. 

Coal per horse-power, 168. 

Combustion, air required for, 39. 

Combustion, heat of, 38. 

Compound condensing engines, dia- 
grams from, 83. 

Compression, 9. 

Compression and clearance, 125. 

Compression and high speed, 128. 

Compression and steam-chest pressure, 
125. 

Compression and terminal pressure, 
128. 

Compression, argument in favor of, 34. 

Compression-curve, 29. 

Compression, too much, 128. 

Condensation, 147. 

Condensation and leaks, loss from, 76. 

Condensation in the cylinder, effect of, 
69, 97. 

Condenser, effect of adding a, 151. 

Condenser, gain by, 82. 

Condenser, necessity of knowing the 
pressure in, 88. 

Condenser, pressure in, 77. 

Condensing and non-condensing dia- 
grams compared, 78, 81. 

Condensing engines, 74. 

Cord, adjusting the length of, 23. 

Cord is best, why a short, 21. 

Cord, stretching of the, 22. 

Cord to use, best, 22. 

Cord, waxing the, 22. 

Cords, hooking together, 24. 

Counter-pressure lines, uneven, 86. 






182 



INDEX. 



Crooked diagrams, unravelling, 101. 
Curves. See Theoretical, etc. 
Curves, agreement of actual and theo- 
retical expansion, 64, 68. 
Cut-off, finding the poit.t of, 61, 
Cut-off, unequalized, 86. 
Cut-off valve behind time, 93. 
Cut-off valve, improper action of, 90. 
Cut-off valve reopens, 99. 
Cut-off, where to, 147. 

Data, how to preserve the, 123. 

Data necessary and useful, 30. 

Decimal equivalents, table of, 167. 

Diagrams, comparing actual and hypo' 
thetical, 134. 

Diagrams from a steam-jacketed cylin- 
der, 74. 

Diagrams from both ends of the cylin- 
der, 12. 

Diagrams from locomotive-engines, 119. 

Diagrams, getting ready to take, 10. 

Diagrams, good features of, 144. 

Diagrams, length of, 21. 

Diagrams, measuring a large number 
of, 170. 

Diagram, names of the lines of the, 28. 

Diagrams, peculiar, 91, 96, 98, 100, 102, 
108, 115. 

Diagram, reading the, 26. 

Diagrams, steam chest, 139. 

Diagrams, taking, 23. 

Diagrams, testing the accuracy of, 24. 

Diagrams, unravelling crooked, 101. 

Drilling the cylinder, 10. 

Drum-motion, 16, 119. 

Drum-motion, examples of, 17. 

Duty, 174, 175. 

Duty, boiler, 39. 

Eccentric out of place, in. 
Economy in the use of steam, 104. 
Economy of expansion, 43. 
Economy of heating feed-water, 164. 
Economy of high-pressure, 44. 
Economy, sfam-engine, 145. 
Elbows, brass, n. 
Elbows, bushing, 11. 
Engines, overloaded, 151. 



Engines, testing, 16S, 177. 
Engines, underloaded, 146. 
Equivalent evaporation, 177. 
Equivalent of heat and work, 38. 
Evaporation, equivalent, 177. 
Evaporation, example of, 40. 
Evaporation, table for reducing, 178. 
Exhaust-closure, early and late, 33. 
Exhaust, heat lost at, 45. 
Exhaust, late, 94. 
Exhaust-line, 29. 
Exhaust-opening, late, in. 
Exhaust, restricted, 90. 
Exhaust-valve, leaky, in. 
Exhausting against pressure, 103. 
Expansion-curve, agreement of actual 

and theoretical, 64. 
Expansion-curve, geometrical method 

of finding points in, 61. 
Expansion-curve, peculiarities of, 95. 
Expansion, economy of, 43. 
Expansion, initial, 131, 133. 
Expansion, initial, economy of, 104. 
Expansion-line, 29. 
Expansion-line, an impossible, 101. 
Expansion, low, 48, 50, 52. 
Expansion of steam, 38, 41. 
Expansion, ratio of, 8. 
Expansion-line and leaky valves, in. 

Feed-water, economy of heating, 64. 
Fly-wheel, effect of increasing capacity 

of, 117. 
Fly-wheel, influence on regulation of, 

148. 
Fly-wheel, light, in. 
Fly-wheel, rule for finding weight of, 

148. 
Foot-pound, 9. 

Forces represented in diagrams, 48. 
Friction, addition for, 174. 
Friction, effect of, 147. 
Friction of indicator-piston, 37. 
Friction of water, 144, 152. 

Gases, temperature of escaping, 39. 
Gauge- pressure, 7. 
Gauges, derangement of water, 174. 
Guide-pulley, 19. 



INDEX. 



183 



Guide-pulleys, disadvantages of, 20. 

Heat, 38. 

Heat and work, 39. 

Heat, available, 45. 

Heat, latent, 9, 40, 164. 

Heat lost at exhaust, 45. 

Heat of combustion, 38. 

Heat, sensible, 9. 

Heat, the unit of, 8. 

Heat-units, 45, 164. 

Heat utilized, 39. 

High-pressure, economy of, 44, 46. 

High-speed diagrams compared with 

moderate speed, 128. 
High-speed reduces area of diagram, 

iSo- 
Holes for indicator, position of, 119. 

Hooking the cords together, 24. 

Horse-power, elements of, 52. 

Horse-power, rinding the, 48, 52, 137. 

Horse-power for one pound mean effec- 
tive pressure, 53. 

Horse power, indicated, 9. 

Horse-power, net, 9. 

Horse-power, water and coal per, 168, 
169, 173. 

Hyperbolic logarithms 4- 1, table of, 166. 

Indicator, care required in use of, 5. 
Indicator, construction and use of the, 1. 
Indicator cylinder, warming, 24. 
Indicator, how to attach the, 10. 
Indicator, how to connect the, 119. 
Indicator-piston, effect of momentum of, 

96. 
Indicators, using one or two, 13. 
Initial expansion, 8, 104, 131, 133. 
Initial expansion, economy of, 104. 
Initial pressure, 7, 127. 

Lap, inside, 79. 

Latent heat, 9, 164. 

Lead, 31. 

Lead, arguments for and against, 32. 

Lead, equalizing, 33. 

Lead, excessive, 33. 

Lead, lack of, 31. 

Lead, unequal, 86. 



Leaky valves by the indicator, detect 

ing, in. 
Levers, length of, 18. 
Levers, reducing, 116. 
Link-motion, claims of loss in the, 133. 
Link-motion, economy of the, 131. 
Locomotive-engines, diagrams from, 119 
Long pipes, 11, 13. 

Mariotte's law, 41. 

Mean effective pressure, 7. 

Mean effective pressure by ordinates or 

divisions, measuring, 51. 
Mean effective pressure, horse-power for 

one pound, 54. 
Mean pressure of expanding steam, 41. 
Measuring diagrams, precautions in, 53. 
Memoranda on diagrams, making, 24. 

Nozzle-area and port-opening, 135. 

Paper, adjusting the, 23. 

Paper-drum, 3. 

Pencil, adjusting the, 23. 

Pencil, neutral position of the, 2. 

Pipes, cleaning, 12. 

Pipes, long, n. 

Piston-displacement, 9. 

Piston, friction of indicator, 37. 

Piston of steam-engine moves between 

two forces, 3. 
Planimeter, measuring mean effective 

pressure by the, 170. 
Port-opening and nozzle-area, 135. 
Pounding, 34. 
Priming, extent of, 174. 
Pumping-engines, duty of, 174. 
Pumping-engines, tests of, 174. 
Pressure, absolute, 7. 
Pressure, back, 7. 
Pressure, boiler, 7. 
Pressure, initial, 7. 
Pressure, mean effective, 7. 
Pressure measured from vacuum, 57. 
Pressure, note on back, 8. 
Pressure of expanding steam, 41. 
Pressure of expanding steam, rule for 

finding, 41. 
Pressure, rapid rise of, 69. 



1 84 



INDEX. 



Pressure, terminal, 7. 
Pressure, total back, 8. 

Ratio of expansion, 8. 

Reducing levers, 16, 119. 

Re-evaporation, 114. 

Reopening of steam-valve, 95. 

Return stroke, 33. 

Rule for finding the mean pressure of 

expanding steam, 42. 
Resistance to motion of the piston of a 

steam-engine, 14. 

Saturated steam, 9. 

Sensible heat, 9. 

Serrated lines, 36. 

Specific volume, 164. 

Springs, care of, 15. 

Springs, how marked, 14. 

Spring to use, proper, 14. 

Steam-chest diagrams, 139. 

Steam, dry, 9. 

Steam exhausted per hour, 67. 

Steam expended by means of Thomp- 
son's table, computing, 70, 135. 

Steam, expansion of, 38, 41. 

Steam, generating, 40. 

Steam-jacketed cylinder, diagrams from 
a, 74. 

Steam-line, 29. 

Steam-line, straight, 104. 

Steam per horse-power per hour, 67. 

Steam-pipes, large and small, 107. 

Steam-ports, large, and balanced valve, 

135- 
Steam-ports, small, 134. 
Steam, pressure of expanding, 41. 
Steam-pressure, working with lower 

and higher, 151, 156. 
Steam, properties of saturated, 159. 
Steam, saturated, 9. 
Steam saved in clearance-space, 6-j. 
Steam, superheated, 9. 
Steam, the conversion of water into, 40. 
Steam-valves, leaky, 111. 
Superheated steam, 9. 

Temperature of escaping gas, 39. 



Terminal pressure, 7, 113. 

Terminal pressure and compression, 128. 

Terminal pressure, high, 76. 

Terminal pressure, theoretical, 7. 

Test, objection to water, 173. 

Tests, different ways of making, 168. 

Tests of pumping-engines, 174. 

Tests, what should be noted in making, 
179. 

Testing engines and boilers, 168. 

Theoretical curve, the, 55. 

Theoretical curve, points from which to 
draw the, 58. 

Theoretical curve, reasons for establish- 
ing, 55- 

Theoretical diagram, 26. 

Thompson's computation-table, 72, 73. 

Throttling-engines, 107. 

Underloaded engines, 146. 
Unit of heat, 8. 
Unit of work, 8. 
Useless work, 146. 

Vacuum-line, establishing, 59. 
Valves, adjusting, 13, 30. 
Valves, detecting leaky, in. 
Valve, improper closing of, 10 
Valve reopens, cut-off, 99. 
Valve, reopening of steam, 95. 
Volume, specific, 164. 

Water, friction of, 141. 

Water into steam, the conversion of, 40. 

Water per horse-power per hour, 169, 

J 73- 
Water-test, objection to, 173. 
Weight of cast-iron, 149. 
Wire-drawing, 8. 
Wire drawing not always objectionable, 

127. 
Wood in coal, equivalent of, 170. 
Work and heat, 39. 
Work done below atmosphere, 76, 82. 
Work in the two ends of the cylinder, 

86. 
Work, the unit of, 9. 
Work, useless, 146. 



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